| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
REVIEW |
1 University of Connecticut, School of Dental Medicine, Department of Oral Health and Diagnostic Sciences, 263 Farmington Ave., Farmington, CT 06030-1710, USA; and
2 Center for Excellence in Oral and Craniofacial Biology, School of Dentistry, Louisiana State University Health Science Center, New Orleans, LA 70119, USA;
* corresponding author, adongari{at}uchc.edu
 |
ABSTRACT |
|---|
 TOP ABSTRACT (1) INTRODUCTION(2) ORAL MUCOSAL CYTOKINE...(3) CYTOKINE AND CELLULAR...(4) THERAPEUTIC PROSPECTS AND...REFERENCES |
|---|
KEY WORDS: oral candidiasis • cytokines • immune response.
|
(1) INTRODUCTION |
|---|
|
TOPABSTRACT(1) INTRODUCTION(2) ORAL MUCOSAL CYTOKINE...(3) CYTOKINE AND CELLULAR...(4) THERAPEUTIC PROSPECTS AND...REFERENCES |
|---|
Candida-associated denture stomatitis affects more than 25% of denture-wearers (Lamy et al., 1999). Also, up to 90% of HIV+ patients have had at least one episode of OPC, and, interestingly, their susceptibility to oral candidiasis is not paralleled by susceptibility to vaginal or disseminated infection (Scully et al., 1994). Although, in recent years, highly anti-retroviral therapy has reduced the incidence of OPC in HIV+ patients, it is still considered unacceptably high (> 15%). In most types of high-risk patients, C. albicans is the main etiologic agent of oral candidiasis (Scully et al., 1994). However, over the last 15 years, new Candida species have emerged as the infectious agents responsible for some of these infections in special-patient categories, such as HIV+ patients, and patients receiving radiation treatment of head and neck tumors (Odds, 1988; Redding et al., 1999). The most commonly reported non-albicans species involved are C. dubliniensis, C. glabrata, C. krusei, and C. tropicalis (Odds, 1988; Redding, 2001). All Candida species form the same type of oral lesion clinically (Redding, 2001); however, recent evidence suggests that mixed infections with more than one species may be associated with more severe symptoms and may be more difficult to treat (Redding et al., 2002).
The host defense mechanisms that control Candida infections are numerous and quite variable within the clinical spectrum of infections caused by this organism, which range from cutaneous, to mucosal, to life-threatening bloodstream infections (Romani, 2004). Both innate and adaptive immunity plays a role in these infections; however, their relative contributions in host protection depend largely on the site of infection. In mucosal infections, innate immunity is very important and is represented by professional phagocytes (neutrophils and monocytes/macrophages), Natural Killer (NK) cells, Dendritic Cells (DC), non-MHC restricted T-cell subsets (
T-cells, some CD8+ T-cells), and non-hematopoietic cells, such as mucosal epithelial cells. There are two main outcomes from the interaction of innate immune cells with Candida: (a) a direct anti-fungal activity; and (b) a regulatory activity that promotes the chemotaxis, proliferation, and terminal differentiation of cells from both innate and adaptive immune systems, through the synthesis of cytokines. Specific innate immune cell-derived cytokines translate into qualitatively different adaptive T helper (Th) cell responses (Th0, Th1, or Th2). In turn, cytokines produced by Candida-specific differentiated Th cells further mobilize and activate phagocytic and non-phagocytic effector cells and provide help for the generation of opsonizing protective antibodies by Candida-specific plasma cells.
It is generally accepted that, for these protective events to take place in fungal infections, the generation of a dominant Th1-cell-type cytokine response, principally represented by interleukin 12 (IL-12) and interferon gamma (IFN), is required (Romani, 2004). IL-12 and IFN are Th1 signature cytokines involved in the activation of antimicrobial functions by innate immune cells (respiratory burst, degranulation, etc.), which also play an instructive role in isotype switching that results in high-quality opsonizing antibodies (reviewed in Johansen and Brandtzaeg, 2004). In contrast, a Th2-biased cell response is usually associated with more severe forms of fungal infections and is characterized by cytokines (mainly IL-4 and IL-5), which are driving eosinophilia, hyper-IgE, and hyper-IgG4 production, which exacerbate the symptomatology and do not protect from fungal infections (Clemons and Stevens, 2001).
Although the above pattern of host cytokine response to Candida infection is generally accepted to play a protective role, over the past few years, evidence has accumulated supporting the fact that protective mechanisms against Candida are not generalizable in all clinical settings, and that immunity to this organism is compartmentalized and site-specific (Fidel, 2002a,b). Thus, we now know that distinct differences exist in the host defense mechanisms that govern susceptibility to vaginal and oral infections, the two mucosal sites most commonly affected by Candida (Fidel, 2002a, b). For example, recent studies in humans have indicated that there is a relative lack of a contribution of systemic or local Th cell responses in the protection of the vaginal mucosa from Candida (Fidel et al., 1993). In contrast, the hallmark of human oropharyngeal infections has been material or functional depletion of systemic and local Th cells by disease or immunosuppressive treatment (Leigh et al., 2001), suggesting that cell-mediated immunity may play a more important role in the oral than the vaginal mucosa.
Because of the high morbidity rate of oropharyngeal candidiasis and the potential for spread to other mucosal sites in the gastrointestinal or respiratory tract, the study of these opportunistic pathogens has become a research priority in recent years. The past decade has thus witnessed an explosion of new information relating to the host protective immunity in Candida infections and the immune regulatory events that occur at the mucosa-fungus interface. This review compiles recent information in the host cytokine responses in oropharyngeal candidiasis and aims to contribute to our understanding of the host cellular and molecular interactions that control Candida infection in the oral mucosa and prevent invasive or disseminated disease. More specifically, in this paper we will address the host cytokine responses to Candida infection as they pertain to the generation of a protective immune response in the oral mucosa.
|
(2) ORAL MUCOSAL CYTOKINE SIGNALS DURING INFECTION |
|---|
|
TOPABSTRACT(1) INTRODUCTION(2) ORAL MUCOSAL CYTOKINE...(3) CYTOKINE AND CELLULAR...(4) THERAPEUTIC PROSPECTS AND...REFERENCES |
|---|
, IL-1ß, IL-8, IL-6, TNF, GM-CSF, and others) regulate leukocyte trafficking, trigger proliferation, and/or activate a vigorous anti-fungal oxidative and non-oxidative metabolic response by these cells. Through these functions, pro-inflammatory cytokines may potentially be involved in immune protection against Candida, as suggested by the finding that fungal pneumonia can occur as a side-effect of anti-TNF therapy (Warris et al., 2001). Although pro-inflammatory cytokines might serve to limit infection, they may also be involved in immunopathology and tissue destruction by activating host matrix metalloproteases, or by provoking uncontrollable leukocyte mobilization and degranulation. Such excessive activation of innate immunoeffectors needs to be prevented, and recovery from fungal infection might depend not only on the activation of effector cell functions, but also on the timely inactivation of these functions and the resolution of the inflammatory process. Transforming growth factor beta (TGF-ß) and IL-10 are anti-inflammatory cytokines that inhibit the secretion of pro-inflammatory cytokines and impair anti-fungal effector functions by phagocytes (reviewed in Romani et al., 2004), thus potentially playing a protective role later in the course of infection, when resolution of the inflammatory process is necessary. A careful balance thus needs to be maintained, not only between the cytokines that affect the cell-mediated immunity to infection (Th1 vs. Th2 cytokines), but also between the pro-inflammatory and anti-inflammatory (Th3 or T regulatory) cytokines released at the site of infection. The salivary, tissue, and cellular cytokine profiles in the oral mucosa during Candida albicans infection are described below.
(2.1) Salivary Cytokine Profiles
Whole saliva is comprised of a mixture of molecules derived from the major and minor salivary glands, the mucosal epithelium, and the serus exudate originating in the gingival crevices (gingival crevicular fluid). Cytokines in saliva are detectable by routine enzyme-linked immunoassays, and are derived from structural mucosal and salivary gland cells (epithelial cells, fibroblasts, endothelial cells), and leukocyte aggregates within the salivary gland tissues, tonsils, and the oral mucosa (including the periodontium). Cytokine profiles in whole saliva can therefore depict the collective state of cytokine responses to infectious agents by all tissues in the oral cavity.
Only one study thus far has compared the cytokine salivary profiles in the immunocompetent host with and without oral candidiasis (Leigh et al., 2002). Results of this study indicated that a mixed Th1/Th2 salivary cytokine profile exists in immunocompetent individuals, with no significant differences between oral candidiasis and healthy groups, suggesting that a local Th cytokine dichotomy in saliva is not associated with susceptibility to infection in the immunocompetent host. Two recent studies examined the salivary cytokine profile in HIV+ individuals with and those without oropharyngeal candidiasis. Unfortunately, the results of these two studies cannot be directly compared, since one study used whole saliva (Leigh et al., 1998), which is more relevant to oropharyngeal infection, and the other study used parotid saliva (Black et al., 2000). Studies by Fidel and co-workers (Leigh et al., 1998) have indicated that HIV infection is driving a shift in the cytokine profile in whole saliva, from a mixed Th1/Th2 to a predominantly Th2-type profile, that seemingly results from a relative reduction of Th1-type cytokines rather than from enhanced production of Th2-type cytokines. Moreover, this group’s pilot analyses of the HIV+ individuals with oropharyngeal candidiasis showed evidence of a more pronounced shift toward a Th2-type cytokine profile (Leigh et al., 1998). In parotid saliva, Katz and co-workers found a mixed constitutive Th1/Th2 cytokine profile in healthy persons; however, this was not significantly altered by HIV infection (Black et al., 2000). Interestingly, all HIV+ patients had somewhat reduced levels of the pro-inflammatory cytokine TNF in parotid saliva, which could potentially be linked to higher susceptibility to infection. In contrast, oral candidiasis significantly elevated Th1-type cytokines (IL-2, IFN) and somewhat decreased the levels of Th2-type cytokines in parotid saliva of HIV+ individuals (Black et al., 2000). This finding is contradictory to the findings of Fidel and co-workers in whole saliva (Leigh et al., 1998) and is somewhat surprising, since, at least in theory, cytokine levels in parotid saliva should not be altered by oropharyngeal candidiasis, an infection that does not spread to the parotid glands. However, the low numbers of patients with oropharyngeal candidiasis examined, the high cytokine variations within patient groups, and the lack of normalization of salivary cytokine content to total protein content in each patient sample make interpretations difficult in this study (Black et al., 2000).
Recently, a chemokine (CCL28) was described which is abundantly and specifically produced by the serous acinar epithelial cells of salivary glands and is secreted in human saliva in high concentrations (Hieshima et al., 2003). Rising evidence suggests that chemotactic cytokines such as CCL28 and endogenous antimicrobial peptides may have substantially overlapping functions. In addition to being a strong chemoattractant for plasma cells into the salivary glands, CCL28 contains a high histidine content in the C-terminal domain that has a potent antimicrobial activity against C. albicans. CCL28 directly attacks the plasma membrane of the micro-organism and generates pores, leading to leakage of cytoplasmic contents (Hieshima et al., 2003). The concentrations of this cytokine in saliva are physiologically relevant, and it is thought to contribute to a natural shield forming over the oral mucosa against colonizing microbes. Currently, it is not known whether the HIV-related salivary gland pathology reduces the levels of this cytokine in saliva, or whether reduced levels of this cytokine may predispose to oral candidiasis; therefore, further investigations are needed in this direction. Another example of the interrelationship between salivary antimicrobial peptides and cytokines is the effect of orally administered lactoferrin, a major anti-fungal product of the serous cells in salivary glands, in a murine model of oral candidiasis (Takakura et al., 2004). The therapeutic activity of lactoferrin in this model was linked to its cytokine-stimulatory effects in cervical lymph node cells, and the significant rise in Th1-type cytokines such as IFN and IL-12, as well as a rise in the pro-inflammatory cytokine TNF, when these cells are challenged with C. albicans (Takakura et al., 2004).
(2.2) Oral Mucosal Tissue Cytokine Profiles
The first study to examine tissue cytokine profiles in oropharyngeal candidiasis (Eversole et al., 1997) characterized the expression of IL-1 and IL-8 in tissue biopsies of HIV– and HIV+ patients with oropharyngeal candidiasis, by immunohistochemistry. IL-1 and IL-8 were found to be present in the parabasilar epithelial cells in both patient groups, and the staining intensity was reported to correlate with the degree of the inflammatory cell infiltration in the submucosa, although no quantitative data were presented to support this conclusion. Sections from the buccal mucosa of HIV– controls with no clinical evidence of candidiasis showed absence of both cytokines. Immunohistochemical studies from a different group also showed elevated levels of IL-18, a T-cell-activating cytokine, in the basal epithelial cell layer in oral candidiasis biopsies, a finding correlating well with the presence of this cytokine in saliva of the infected individuals (Tardif et al., 2004).
Recently, Fidel and co-workers conducted a quantitative analysis of a wide range of tissue-associated cytokines, at the mRNA expression level, in HIV+ patients, directly at the site of Candida infection (Lilly et al., 2004). Results from this study showed that HIV infection in the asymptomatically colonized host enhanced mRNA expression of most chemokines examined, but had little effect on other cytokines. Subjects with oropharyngeal infection had increased levels of IL-2, IL-10, IL-15, IFN, IL-6, MCP-1, IP-10, and RANTES in the oral mucosa, compared with levels in asymptomatically Candida-colonized subjects without candidiasis. In contrast, expression of IL-8, a neutrophil chemoattractant, was not elevated in these lesions. Finally, tissues from HIV+ subjects with oropharyngeal candidiasis exhibited IL-1 levels that did not reach the ‘baseline’ HIV– tissue levels, and had decreased levels of TNF (Lilly et al., 2004). Interestingly, in a mouse model of oropharyngeal C. albicans infection, resembling the pseudomembranous type of infection seen in HIV+ patients, TNF mRNA was discovered only in the oral mucosa of recovering mice (Farah et al., 2002b).
(2.3) In vitro Oral Mucosal Systems
(2.3.1) Single-cell Systems
In oral mucosal infections, C. albicans organisms colonize the outermost layers of epithelium, rarely invading past the spinous cell layer (Reichart et al., 1995; Eversole et al., 1997). Although the role of epithelial cells as an infection barrier against Candida is well-recognized (Hahn and Sohnle, 1988), new information is emerging about the role of these cells in orchestrating the oral mucosal inflammatory response to this pathogen by synthesizing pro-inflammatory and immunoregulatory cytokines. Much of this new information is derived from in vitro studies with oral epithelial cells from various sources used as models of infection.
Several approaches have been used to study the oral epithelial cell-Candida interactions in vitro, one of the simplest being the use of buccal epithelial cells isolated from unstimulated saliva (Steele and Fidel, 2002). However, these are terminally differentiated, short-lived, cell populations, which are generally expected to have a metabolic capacity lower than that of actively growing cells in vivo or in vitro. Indeed, most of the primary oral epithelial cells in these studies were also relatively unresponsive to certain stimuli used as positive controls. Monolayer cultures of human oral epithelial cells from squamous cell carcinomas (SCC cell lines) or primary gingival keratinocytes have also been used as models of infection (Dongari-Bagtzoglou and Kashleva, 2003a, b; Dongari-Bagtzoglou et al., 2004). When cell lines from carcinomas are used, it is generally accepted that the cellular responses to infection of a single cell line should be confirmed with multiple cell lines, and even then, results should be interpreted with caution, since they may not always accurately reflect the responses of normal epithelial cells. Working with ‘normal’ primary oral epithelial cell monolayer cultures (e.g., gingival keratinocytes), as opposed to cell lines, is also limited by the fact that these cells lack a polarized phenotype, have a lower differentiation level, and lack a large number of cell-cell contacts, which affects their function and responses to external stimuli (Radyuk et al., 2003). Nevertheless, this approach has provided some interesting data (Dongari-Bagtzoglou and Kashleva, 2003a; Dongari-Bagtzoglou et al., 2004), some of which (e.g., IL-8 and IL-1 stimulation by C. albicans) has been supported by findings in human tissue biopsies from infected individuals (Eversole et al., 1997).
Three-dimensional culture systems of oral epithelial cells have been developed to provide a differentiation level that is closer to that of mucosal cells in vivo. Investigators’ ability to grow oral epithelial cells in a multilayered culture on microporous membranes as a three-dimensional model of oral mucosa has added another useful tool for exploring Candida-oral epithelial cell interactions (Schaller et al., 2002, 2004). In this model, an oral epithelial cell line was grown at the air-liquid interface in a chemically defined medium to form an oral epithelial tissue devoid of the keratin layer. This model system more closely approximates the ‘lining’ non-keratinized oral mucosa, such as the labial and buccal mucosa, and does not ultrastructurally resemble the palatal mucosa, which is one of the most common sites of oral infection. Nevertheless, this model has the advantage of simultaneously monitoring epithelial cell tissue damage and tissue invasion by the micro-organism, together with the expression of certain host cytokines in situ (Schaller et al., 2002). Nonetheless, this model mucosa was generated with the use of a cancer cell line, and the same cautions regarding generalizing results to normal epithelial tissue apply here as well. In addition, this model system cannot account for possible interactions between different tissues or cell types during the infectious process in the oral mucosa in vivo.
Studies with the oral epithelial cell infection models described above identified an array of pro-inflammatory cytokines—namely, IL-1, IL-1ß, IL-8, IL-18, TNF, and GM-CSF—that are generated from the interaction of these cells with the organism (Rouabhia et al., 2002; Schaller et al., 2002; Steele and Fidel, 2002; Dongari-Bagtzoglou and Kashleva, 2003a,b; Dongari-Bagtzoglou et al., 2004). These cytokine responses of oral epithelial cells to C. albicans infection are strain-specific, require direct epithelial cell-fungal cell contact, and are optimal when viable yeasts, germinating into hyphae, are used in cell interactions (Schaller et al., 2002; Dongari-Bagtzoglou and Kashleva, 2003a,b). Strong evidence also supports the fact that IL-1, resulting from the interactions of oral epithelial cells with C. albicans, autoregulates other cytokines secreted in response to this pathogen (Dongari-Bagtzoglou and Kashleva, 2004).
Interleukin-1 (IL-1) is a major constitutive and inducible pro-inflammatory product of epithelial cells, which can act as a key cytokine to amplify the inflammatory response by neighboring mucosal cells, or activate local leukocyte antifungal activities (reviewed in Dinarello, 1997). Studies screening cell supernatants or lysates of C. albicans-infected oral epithelia (grown in monolayers or three-dimensional multilayer cultures), for various pro-inflammatory cytokines, have identified IL-1 as one of the major cytokines up-regulated at both the mRNA and protein levels (Schaller et al., 2002; Dongari-Bagtzoglou et al., 2004). Dongari-Bagtzoglou and co-workers have shown that Candida-infected oral epithelial cells release this pro-inflammatory cytokine in its mature protein form in their microenvironment upon cell lysis. It has been hypothesized that most of the IL-1 processing in the epithelial cell-C. albicans co-culture system takes place at the plasma membrane, where the cytolytic actions of C. albicans phospholipases and proteases trigger a release of membrane phospholipids. In turn, membrane phospholipids may activate the IL-1 convertase, which cleaves membrane-associated pro-IL-1 and triggers the release of the mature protein in culture supernatants (Kobayashi et al., 1990). Similarly, the ability of C. albicans to induce cleavage of the inactive IL-18 pro-peptide and trigger release of the active mature IL-18 protein has been demonstrated, an event temporally associated with the presence of the active form of the IL-1 convertase in these cells (Rouabhia et al., 2002). IL-1 released by injured epithelial cells increases the pro-inflammatory cytokine production (IL-8, GM-CSF) by neighboring uninfected mucosal and stromal cells (Dongari-Bagtzoglou et al., 2004). Such a mechanism could serve to amplify and extend the local inflammatory response, even in the absence of direct fungal invasion of the deeper mucosal and submucosal tissues.
Only live, germinating organisms are capable of stimulating pro-inflammatory cytokine responses by oral epithelial cells, consistent with reports in endothelial cells (Orozco et al., 2000; Schaller et al., 2002; Dongari-Bagtzoglou and Kashleva 2003a, b). C. albicans is a polymorphic organism which undergoes morphological transition among yeast, pseudohyphal, and hyphal forms. All three morphogenetic forms of C. albicans are frequently encountered in the oral mucosa (Cox et al., 1996), and, in most oral infections, both yeast and filamentous organisms can be found in the infected tissues (Olsen et al., 1977). Although, in animal models of disseminated infection, it has been established that the ability to change from yeast to hyphae is crucial for virulence (Saville et al., 2003), the exact role of hyphal transition during the development of oral candidiasis is still unclear. However, clinicopathologic findings have correlated the presence of filamentous forms with localized tissue invasion in oral candidiasis (Reichart et al., 1995; Cox et al., 1996). Recently, Dongari-Bagtzoglou and co-workers studied the interactions of oral epithelial cells with the three different morphotypes of this pathogenic organism (Villar et al., 2004). More specifically, they compared the ability of yeast, pseudohyphal, and hyphal organisms to adhere to and damage oral epithelial cells, as well as their ability to trigger a pro-inflammatory cytokine (IL-8, IL-1) response. By the use of mutant strains with defects in hyphal transformation, or by the application of environmental pressure which affected filamentation in wild-type organisms, it was determined that morphogenesis is an important factor in the outcome from the interactions between oral epithelial cells and C. albicans. When germination-deficient C. albicans mutants that form yeast exclusively (efg1/efg1/cph1/cph1 mutant; Lo et al., 1997) or pseudohyphae (tup1/tup1 mutant; Braun and Johnson, 1997) were co-cultured with oral epithelial cells, they exhibited a significantly reduced capacity to adhere to oral epithelial cells and disrupt their cell membrane. Also, in sharp contrast to strains which formed true hyphae under these co-culture conditions, germination mutants and oral strains naturally deficient in germination triggered essentially no pro-inflammatory cytokine responses by these cells (Villar et al., 2004).
In addition to morphogenesis, the invasive capacity of different C. albicans strains dramatically influences the oral epithelial cell pro-inflammatory cytokine response to infection. It was recently shown that highly invasive C. albicans strains trigger a wider array and higher levels of pro-inflammatory cytokines in oral epithelial cells compared with invasion-deficient organisms that have similar germination patterns in vitro (Villar et al., 2005).
(2.3.2) Multi-cell-type Systems
The biggest limitation of in vitro single-cell systems as models of infection is that they lack many characteristics of native mucosae, such as polarized cell phenotype, differentiation level, and metabolic responses to external stimuli. Therefore, the responses of these cultures in vitro may not accurately represent their responses in vivo. To overcome some of these limitations, investigators recently used an artificial tissue culture system of infection, incorporating oral epithelial cells and fibroblasts, in an attempt to mimic the oral masticatory mucosa and submucosa. Results in this system confirmed that live, but not killed, C. albicans induced increased levels of IL-1ß, IL-1, IL-8, IL-18, GM-CSF, and TNF in the engineered oral mucosa, as noted in single-cell-type systems, and IL-6 was added to this list of pro-inflammatory cytokines (Dieterich et al., 2002; Moustefaoui et al., 2004a,b; Tardif et al., 2004). One interesting finding from such three-dimensional oral mucosal/submucosal systems, in studies by two independent groups of investigators, was that, in this setting, oral epithelial cells can be stimulated by C. albicans to secrete IFN, an immunoregulatory and phagocyte-activating cytokine traditionally thought to be produced only by T-cells and NK cells (Schaller et al., 2004; Tardif et al., 2004).
Schaller and co-workers incorporated an immunological component in a modification of this three-dimensional mucosal system by adding peripheral blood neutrophils (Schaller et al., 2004). In elegantly performed in vitro experiments, this group showed that C. albicans-infected epithelial cells produced increasing amounts of IFN, TNF, IL-1, IL-1ß, IL-6, and IL-8, whereas IL-10 was not affected. In the presence of transepithelially migrating neutrophils, the levels of the pro-inflammatory cytokines IL-1, IL-1ß, IL-6, GM-CSF, and IL-8 increased further. In addition, concomitant strong expression of neutrophil-activating cytokines (GM-CSF, IL-6, and IL-8) in the mucosal epithelium was linked to transepithelial neutrophil migration in these experiments (Schaller et al., 2004).
|
(3) CYTOKINE AND CELLULAR CORRELATES OF MUCOSAL PROTECTION IN OROPHARYNGEAL CANDIDIASIS |
|---|
|
TOPABSTRACT(1) INTRODUCTION(2) ORAL MUCOSAL CYTOKINE...(3) CYTOKINE AND CELLULAR...(4) THERAPEUTIC PROSPECTS AND...REFERENCES |
|---|
, IL-8 and GM-CSF by oral epithelial cells and fibroblasts in response to Candida (Dongari-Bagtzoglou et al., 1999; Schaller et al., 2002; Dongari-Bagtzoglou and Kashleva, 2003a, b) could explain the histopathologic finding of neutrophilic micro-abscesses in these lesions, since these cytokines are potent chemoattractants and/or activators of PMNs (Baggiolini et al., 1989; Blanchard et al., 1991). In HIV+ patients, neutrophils appear to be a rare finding in oral candidiasis lesions and are encountered only in a limited number of erythematous forms. This is consistent with the lack of the neutrophil chemoattractant IL-8 in these sites, as shown by Fidel and co-workers (Lilly et al., 2004). The inflammatory cell infiltrate is primarily mononuclear in both pseudomembranous and erythematous cases of HIV-associated infection (Romagnoli et al., 1997). Few Candida hyphae are associated with the atrophic epithelium in erythematous candidiasis, whereas numerous organisms are found invading the prickle cell layer of oral epithelium in pseudomembranous candidiasis. In one study, CD1a+ dendritic cells were the only cell type to be significantly increased in HIV+ oral candidiasis, as compared with HIV+ or HIV– controls. These cells were almost exclusively restricted to the basal layer of the oral epithelium. Overall, a change in localization of these cells, from the lamina propria into the basal epithelial cell layer, was noted, as opposed to an increase in cell number (Romagnoli et al., 1997).
CD8+ lymphocytes appear to have a central role in the immune response in HIV-associated OPC. In addition to CD1a+ cells, Romagnoli and co-workers identified CD8+ cells as one of the principal cell types infiltrating erythematous lesions (Romagnoli et al., 1997). Interestingly, a murine AIDS model (MAIDS) showed a rate of 30% recurrent OPC in inoculated mice, with a predominance of CD8+ T-cells recruited into the tissues (Deslauriers et al., 1997). A more recent immunohistochemical analysis of the T-cell populations in HIV-associated oral candidiasis in humans showed few to no CD4+ T-cells, an intriguing accumulation of high numbers of CD8+ T-cells at the lamina-propria-epithelium interface of the infected sites, as compared with uninfected controls, and a positive correlation between the numbers of CD8+ T-cells and the oral fungal burden in HIV+OPC– individuals (Myers et al., 2003). The same group later described a lack of correlation between cytokine mRNA levels and CD4+ T-cell blood counts, which is consistent with the relative absence of these cells from the oral lesions in these patients (Myers et al., 2003; Lilly et al., 2004). In contrast, the increased levels of IL-2 and IL-15—two cytokines involved in the differentiation and effector function of CD8+ T cells—found in the infected oral tissues, together with the elevation of the CD8+ cell chemokines RANTES and IP-10 (Lilly et al., 2004), are consistent with the increased presence of CD8+ T-cells in the lesions of these patients (Myers et al., 2003).
The accumulation of CD8+ T-cells at the lamina-propria-epithelium interface of the infected sites may suggest a potential problem in cell trafficking, promoting susceptibility to OPC in HIV+ individuals. Cellular migration is controlled by heterodimer homing receptors made up of single-chain integrins, and reciprocal adhesion molecules present on tissue. In recent immunohistochemical studies, the CD8+ T-cells present in both OPC– and OPC+ tissue had positive integrin expression, and there was no discernible difference in OPC– vs. OPC+ tissue, except for the increased number of cells in OPC+ tissue with homing receptors (McNulty et al., 2005). Thus, there appears to be no deficiency in homing receptors on the CD8+ T-cells. In contrast, there were differences in tissue adhesion molecule expression. MAdCAM expression was increased in OPC+ tissue in support of the increased presence of T-cells. E-cadherin, on the other hand, was significantly decreased in the epithelium of OPC+ tissue (McNulty et al., 2005). Therefore, the decrease in E-cadherin may limit the ability of the CD8+ T-cells to migrate to the outer part of the epithelium, where Candida is primarily located. This would provide a reasonable explanation for the accumulation of cells at the lamina-propria-epithelium interface and may play a role in the susceptibility of HIV+ individuals to OPC.
(3.2) Role of Oral Epithelial Cells as Innate Immune Cells
Oral mucosal epithelial cells are constantly exposed to microbial challenge and therefore play an important role as the first line of defense against infection (Fig.
). The importance of this cell type in fighting oral fungal infection is suggested by the fact that autologous skin grafts, transplanted into the oral cavity to reconstruct tissue defects after radical resection of oral cancer, are known to be frequently infected with C. albicans (Katou et al., 2001). In several studies, oral epithelial cells have been shown to have the potential for direct anti-candidal activity. In addition to synthesis of natural antibiotic peptides (i.e., calprotectin and defensins) with antifungal activity (Sohnle et al., 1991; Krisanaprakornkit et al., 2003), an acid-labile, contact-dependent oral epithelial cell anti-Candida activity has recently been described, postulated to be mediated by a carbohydrate moiety, which was significantly greater than that of vaginal epithelial cells (Steele et al., 2001; Nomanbhoy et al., 2002). This antimicrobial activity extended to other Candida species, including C. glabrata, C. dubliniensis, and C. krusei. Saliva appeared to have no effect on growth inhibition, and cells isolated from HIV+ patients with OPC had reduced antifungal activity as compared with that in HIV+OPC– controls (Steele et al., 2000). Analysis of more recent data, however, provides substantial evidence that disproves a role for carbohydrates in contact-dependent oral epithelial cell anti-Candida activity (Yano et al., 2005). It was also shown that the antifungal activity is static and dependent on cell contact by intact, but not necessarily live, epithelial cells (Yano et al., 2005).
|
, promote the killing of C. albicans by these cells (Csato et al., 1990). In addition, pro-inflammatory cytokines have a well-established role in augmenting both the calprotectin and ß-defensin synthesis by epithelial cells in vitro (Brandtzaeg et al., 1995; Dale et al., 2001).
The interaction of mucosal epithelial cells with phagocytes has a synergistic effect in the elimination of bacterial pathogens, mediated by the presence of cytokines (Goodrum and Poulson-Dunlap, 2002). Along these lines, Dongari-Bagtzoglou and co-workers recently showed that oral epithelial cells can up-regulate PMN anti-candidal activity in vitro (Dongari-Bagtzoglou et al., 2005). Hyphal growth inhibition experiments with human PMN from multiple donors revealed that the antifungal activity of PMN can be enhanced by two- to three-fold over basal levels by C. albicans-infected oral epithelial cell supernatants, an effect largely dependent on the presence of bioactive IL-1 in these supernatants (Dongari-Bagtzoglou et al., 2005).
(3.3) Role of Professional Phagocytes in OralCandida Clearance
The sequential recruitment of phagocytes (neutrophils and macrophages) toward infected mucosal sites is the most fundamental process of innate mucosal immunity. Neutrophils are typically the first and perhaps the most abundant leukocytes to be recruited in Candida infections (Ashman and Papadimitriou, 1995). Homing of neutrophils into the oral epithelium requires extravasation from the capillaries through an endothelial cell layer, followed by migration into the epithelial compartment. The initial neutrophil-epithelial interactions involve 2 integrin binding (especially CD11b/18) on neutrophils to an unidentified ligand on mucosal epithelial cells (Parkos, 1997). Subsequent movement through epithelium requires epithelial CD47-mediated interactions with PMN-expressed signal regulatory protein (Liu et al., 2002). Cross-talk between mucosal epithelial cells and phagocytic cells in a co-culture system in vitro has been demonstrated via the release of soluble factors that augmented the inflammatory response to infection (Goodrum and Poulson-Dunlap, 2002). Pro-inflammatory cytokines such as TNF enhance the adhesive interactions between PMN and epithelial cells and may aid in transepithelial migration (Tosi et al., 1994).
Because transepithelial migration of neutrophils is a histological hallmark of most oral candidiasis lesions, neutrophils are believed to play an important role in the clearance of this pathogen (Challacombe, 1994; Eversole et al., 1997). This is further supported by the fact that patients with defects in neutrophil numbers or function are more susceptible to oral infection with this micro-organism (Epstein et al., 2003; Myoken et al., 2004). Also, severe salivary PMN hypofunction (reduced superoxide generation and candidacidal activity) has been described in patients with oral candidiasis (Ueta et al., 2000) and in high-risk individuals, such as cancer patients receiving chemoradiotherapy (Ueta et al., 1993), or the elderly (Tanida et al., 2001), and salivary PMN hypofunction may thus be considered a possible risk factor for oral candidiasis.
A comparison of the candidacidal activity among leukocytes in vitro suggests that neutrophils have the highest capacity to kill this organism (Lehrer and Cline, 1969). Although PMNs are capable of killing fungal targets without help from exogenously provided cytokines in vitro (Lehrer and Cline, 1969), there are conflicting data about the role of neutrophils and neutrophil-activating cytokines in the protection from oral Candida infection in murine models of oropharyngeal infection in vivo (Farah et al., 2001). It appears that, in CD4+ T-cell-deficient mice, phagocytic cells alone were not adequate for resolving the oral infection, unless the animals were reconstituted with naïve syngeneic T-cells (Farah et al., 2002a). Thus, it is possible that, in murine candidiasis, T-cells are needed to produce phagocytic cell chemotactic and activating cytokines for efficient infection resolution by professional phagocytes. Nevertheless, invasive oral infection in otherwise immunocompetent mice was demonstrated in certain strains of mice studied by a combined neutrophil and macrophage depletion approach, implying a synergistic role for these phagocytic cell types in clearing the oral infection (Farah et al., 2001).
More supportive evidence for an active role for neutrophils in the mucosal clearance of C. albicans has recently emerged from a three-dimensional in vitro model of oral candidiasis supplemented with human peripheral blood neutrophils (Schaller et al., 2004). In the presence of neutrophils, a significant reduction in C. albicans tissue penetration and damage was observed, which corresponded to significant reductions in LDH release, used as a marker of epithelial cell injury. Curiously, this protective effect was also seen when direct physical contact between PMNs and C. albicans was prevented, suggesting that reciprocal regulation of epithelial-cell-mediated anti-candidal activity by PMNs was taking place, rather than direct killing of C. albicans by neutrophils (Schaller et al., 2004).
Several investigations have provided evidence to support the notion that increased susceptibility to candidiasis in HIV+ subjects may be at least partly due to a failure of PMN activation by cytokines upon encounter with the fungus (Nielsen et al., 1986; Ellis et al., 1988). Defective ex vivo PMN activation has been reported in patients at later stages of HIV infection. Although studies of oxidative metabolism have been conflicting, reduced chemotaxis and bacterial or fungal phagocytosis and killing have consistently been reported (Ellis et al., 1988; Murphy et al., 1988; Roilides et al., 1990; Coffey et al., 1998). Functional impairment of PMN has been shown to be more profound in patients with a longer course of HIV infection and had a strong inverse relationship with the absolute CD4 cell count (Pitrak et al., 1993; Brettle, 1997). Since PMNs are not directly susceptible to HIV infection, several investigators have proposed that defective PMN function is attributed, at least in part, to the relative decrease in PMN-activating growth factors and cytokines normally produced by CD4+ T-cells, monocytes, and macrophages, all of which gradually succumb to direct HIV infection (Pitrak et al., 1993; Coffey et al., 1998). In support of this hypothesis, both in vivo and in vitro studies have shown that defective PMN function in HIV patients could be corrected by treatment with exogenously provided cytokines or growth factors (Roilides et al., 1990; Meyer and Nielsen, 1996; Coffey et al., 1998). Thus, if a protective role of PMNs in the oral micro-environment is accepted, these observations may partly explain the increased susceptibility of HIV+ patients to oral candidiasis. Conversely, since PMN activation does not contribute to the clearance of vaginal infection, but instead may exacerbate its symptomatology (Fidel, 2004), there is a lack of increased susceptibility of HIV+ patients to vaginal candidiasis (reviewed in Fidel, 2002a,b).
(3.4) Role of Cell-mediated Immunity
One of the hallmarks of oropharyngeal candidiasis is the high prevalence of infection when the CD4+ T-cell subset is lower than 200 cells/µL (reviewed in Fidel, 2002a). However, in a large study evaluating systemic Candida-specific cell-mediated immunity (delayed skin test reactivity, lymphocyte proliferation, and Th1/2 cytokines) in those with or without oral infection, it was determined that there were no deficiencies in these responses in patients with oral infection (Leigh et al., 2001). These results, although unexpected, were also supported by a study, from a different group, showing no deficiencies in responses of T-cell clones to Candida antigens in HIV+ patients with oral infection (Kunkl et al., 1998). As an explanation for the strong correlation of oropharyngeal infection to reduced CD4+ T-cells in light of these discrepant findings, it was hypothesized that a threshold number of systemic CD4+ T-cells is required to protect the oral mucosa, below which, protection is solely dependent on local mucosal defenses (Fidel, 2002a,b). In addition, most animal studies have supported a dominant role for CD4+ T-cells in host defense against oral Candida by showing increased or persistent oral Candida infection when CD4+ cells are missing (Deslauriers et al., 1997; Farah et al., 2002a,b). When CD4+ T-cells were reconstituted in these animals, oral infection resolved, and this coincided with the presence of Th1-type cytokines in the cervical lymph nodes (Elahi et al., 2000; Farah et al., 2002a).
As noted above, a significant increase in the number of CD8+ cells was reported in C. albicans-infected oral tissues of HIV+ individuals with fewer than 200 CD4+ T-cells/µL (Myers et al., 2003). The origin of these CD8+ T-cells is currently unknown, although recent studies by Fidel and co-workers have showed that the CD8 antigen was comprised of the standard and ß chain heterodimer (McNulty et al., 2005), which is thymically derived, rather than the chain homodimer often found on CD8+ cells in gastrointestinal tissue, which are thought to be extra-thymically derived (Rocha et al., 1994; Yamada et al., 1999). The functional role of these cells in oral candidiasis is currently unknown; however, it is tempting to speculate that they may be directly involved in the clearance of the micro-organisms acting as innate effectors in an MHC-unrestricted manner, similar to the IL-2-activated CD8+ cells in mice (Beno et al., 1995). Interestingly, a similar non-MHC-restricted anti-candidal activity in peripheral blood CD8+ lymphocytes has been described in HIV+ patients with a recent episode of oropharyngeal candidiasis (Colon et al., 1998).
NK cells have been suggested to maintain a central role in the defense against Candida, since they provide activating signals to PMN through the release of specific cytokines (Ashman and Papadimitriou, 1995). Although NK cells are unable to kill C. albicans directly in vitro (Djeu and Blanchard, 1987; Zunino and Hudig, 1988; Arancia et al., 1995), in a mouse model of OPC these cells could substitute for T-cells in phagocytic cell activation and protected the animals from lethal oral infection (Balish et al., 2001).
(3.5) Role of Humoral Immunity
The role of humoral immunity in resistance or susceptibility to oropharyngeal candidiasis in humans is uncertain, and has been studied mostly in the clinical setting of HIV infection (reviewed by Fidel, 2002a,b). An early study examining the effects, in immunocompetent subjects, of Candida-specific antibodies on the interactions between the fungus and the oral mucosa concluded that titers of antibodies in saliva reflected the degree of local antigenic stimulation, being significantly higher in candidiasis than in uninfected controls or healthy carriers (Epstein et al., 1982). Also, a significant inverse correlation was found between salivary IgA anti-Candida antibody content and the adherence of the organism to buccal epithelial cells, suggesting a role of IgA in inhibiting colonization, although the majority of the antibodies detected in saliva were not able to inhibit adherence (Epstein et al., 1982).
Several earlier studies examining salivary antibody levels in HIV+ patients have reported contradictory findings showing either elevated or reduced anti-Candida IgA in saliva of patients with oropharyngeal candidiasis (Wray et al., 1990; Coogan et al., 1994). In these earlier studies, lack of normalization of the data to either total protein or total immunoglobulin content makes interpretation difficult. A recent comprehensive analysis of Candida-specific antibodies in the saliva of HIV+ patients with and without oral candidiasis, with a large cohort of patients, strict patient stratification, and appropriate normalization of the data, showed no differences in antibody levels, suggesting little or no role for antibodies in the protection against Candida (Wozniak et al., 2002). Although results of this study appear to be more conclusive, they are based on the analysis of the full complement of anti-Candida antibody levels in saliva, including protective, indifferent, and potentially harmful antibodies. Therefore, the possibility still remains that protective antibodies are reduced in patients with oral infection and are replaced by non-protective or indifferent antibodies, as has been suggested elsewhere (Fidel, 2002a,b).
A study that specifically addressed serum and salivary antibody levels against adhesion-related (mannoproteins) or tissue invasion antigens (Sap1 and Sap6) in HIV+ patients showed that such presumably protective salivary antibodies were increased in oral candidiasis. To explain the lack of protection in the presence of such antibodies, the authors suggested that there is a critical concentration threshold of fungi, beyond which salivary antibodies are ineffective (Drobacheff et al., 2001).
The induction of humoral immunity, as indicated by high levels of IL-4 in regional lymph nodes and high levels of systemic IgG and IgA antibodies, appeared to play a protective role in a mouse model of oral candidiasis, since neutralization of IL-4 resulted in delayed clearance of fungi (Elahi et al., 2000). In general, cytokines play important roles in the expansion and terminal differentiation of mucosal immunoglobulin-producing plasma cells (reviewed in Johansen and Brandtzaeg, 2004). For example, transforming growth factor ß (TGF-ß) is considered to be essential in class-switch recombination to IgA. Moreover, in the intestinal mucosa, the polymeric immunoglobulin receptor, which facilitates the translocation of polymeric sIgA and sIgM antibodies, is transcriptionally regulated by cytokines such as IFN, TNF, and IL-4 (Blanch et al., 1999). Thus, during low-grade inflammation, induced by subclinical Candida infection, these cytokines may provide a regulatory link among secretory immunoglobulin production, export, and oral mucosal clearance of the pathogen.
|
(4) THERAPEUTIC PROSPECTS AND FUTURE DIRECTIONS |
|---|
|
TOPABSTRACT(1) INTRODUCTION(2) ORAL MUCOSAL CYTOKINE...(3) CYTOKINE AND CELLULAR...(4) THERAPEUTIC PROSPECTS AND...REFERENCES |
|---|
). As a result, the oral mucosa is chronically inflamed with intense intra-epithelial and subepithelial infiltration by leukocytes (Reichart et al., 1995; Eversole et al., 1997; Myers et al., 2003). Since leukocytes establish contact with the micro-organisms only within the epithelial cell layer, it is likely that modulation of the fungicidal mechanisms of these cells by various epithelial cytokines significantly affects the ability of the host to clear this infection. Further studies are needed to demonstrate that induction of specific cytokines in oral epithelial cells in vivo may promote PMN, monocyte, and/or keratinocyte antifungal activities.
One strategy to control fungal infection in severely immunocompromised hosts is to improve the immune effector functions of cells involved in the clearance of the micro-organism by the use of cytokine-based therapeutics as adjuncts to traditional anti-fungal drugs. Cytokine treatment, combined with white blood cell transfusions, has been successfully tested in neutropenic patients with refractory invasive fungal infections (Rodriguez et al., 1998). Also, IFN treatment restored resistance to fungal infections in patients with chronic granulomatous disease, and improved the efficacy of antifungal chemotherapy when used as an adjunct (Roilides et al., 2002).
GM-CSF is a cytokine which augments neutrophil antifungal activities in vitro and may have a protective function in oral candidiasis in vivo. It has been reported that administration of rhGM-CSF, as adjunctive treatment of fluconazole-refractory oropharyngeal candidiasis in AIDS patients, exerts a significant beneficial effect on the oral mycoflora, and may help clear the infection in these patients (Vazquez et al., 2000). Multiple other pro-inflammatory cytokines—such as IL-1, IL-1ß, IL-8, TNF, and IL-15—can augment the neutrophil candidacidal functions in vitro and could therefore provide future pharmacological targets in anti-fungal drug-resistant forms of oral candidiasis in vivo. In addition, if a protective role for CD8+ T-cells in HIV-related OPC is assumed, cytokines enhancing CD8+ T-cell mobilization toward infected sites, or up-regulating adhesion molecule expression (e.g., E-cadherin) in the infected mucosal tissues, may also provide useful therapeutic targets in this patient category.
Several studies have provided a link between lower levels of TNF in the oral tissues or saliva of humans and animals with oral C. albicans infection (Black et al., 2000; Farah et al., 2002b; Lilly et al., 2004), suggesting that reduced levels of this cytokine may be involved in susceptibility to oral infection. TNF has been shown to be protective in murine-disseminated candidiasis (Allendoerfer et al., 1993), and has been suggested to be essential for granulocyte antifungal activity in vivo (Steinshamn and Waage, 1992). Moreover, TNF knock-out mice are highly susceptible to systemic candidiasis, since absence of this cytokine impairs neutrophil recruitment and effective phagocytosis of C. albicans (Netea et al., 1999). Future animal studies are needed to examine the effect of TNF ablation on the course of oral candidiasis in vivo, and to evaluate the potential for this cytokine as a local immunotherapeutic adjunct in oropharyngeal candidiasis in humans.
In conclusion, the identification of cytokines with the ability to enhance anti-fungal activities of immune effector cells is important, since it may have therapeutic implications in the treatment of this oral infection in the severely immunocompromised host. For example, topical use of specific recombinant cytokines with neutrophil-activating potential, in combination with anti-fungal agents, may become the future treatment of choice in the extremely immunocompromised host suffering with oropharyngeal candidiasis. Because cytokines in complex mixtures can elicit biological effects that are different from those of each cytokine in isolation, studying ‘global’ patterns of cytokine expression in the future is more likely to yield information more biologically relevant and clinically useful than that provided by the conventional assays, used so far, that detect single cytokines. Therefore, currently, there is a need for the application of high-throughput approaches to evaluate cytokine responses to C. albicans infection, coupled with improved animal- or tissue-engineering models of oral infection, where the effects of combinations of multiple cytokines in the clearance of the micro-organism can be tested.
|
ACKNOWLEDGMENTS |
|---|
Received November 30, 2004; Accepted April 20, 2005
|
REFERENCES |
|---|
|
TOPABSTRACT(1) INTRODUCTION(2) ORAL MUCOSAL CYTOKINE...(3) CYTOKINE AND CELLULAR...(4) THERAPEUTIC PROSPECTS AND...REFERENCES |
|---|
Arancia G, Molinari A, Crateri P, Stringaro A, Ramoni C, Dupuis ML, et al. (1995). Noninhibitory binding of human interleukin-2-activated natural killer cells to the germ tube forms of Candida albicans. Infect Immun 63:280–288.[Abstract]
Ashman RB, Papadimitriou JM (1995). Production and function of cytokines in natural and acquired immunity to Candida albicans infection. Microbiol Rev 59:646–672.
Axéll T, Samaranayake LP, Reichart PA, Olsen I (1997). A proposal for reclassification of oral candidosis. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 84:111–112.[ISI][Medline]
Baggiolini M, Walz A, Kunkel SL (1989). Neutrophil-activating peptide-1/interleukin 8, a novel cytokine that activates neutrophils. J Clin Invest 84:1045–1049.
Balish E, Warner T, Pierson CJ, Bock DM, Wagner RD (2001). Oroesophageal candidiasis is lethal for transgenic mice with combined natural killer and T-cell defects. Med Mycol 39:261–268.[ISI][Medline]
Beno DW, Stover AG, Mathews HL (1995). Growth inhibition of Candida albicans hyphae by CD8+ lymphocytes. J Immunol 154:5273–5281.[Abstract]
Black KP, Merrill KW, Jackson S, Katz J (2000). Cytokine profiles in parotid saliva from HIV-1-infected individuals: changes associated with opportunistic infections in the oral cavity. Oral Microbiol Immunol 15:74–81.[ISI][Medline]
Blanch VJ, Piskurich JF, Kaetzel CS (1999). Cutting edge: coordinate regulation of IFN regulatory factor-1 and the polymeric Ig receptor by pro-inflammatory cytokines. J Immunol 162:1232–1235.
Blanchard DK, Michelini-Norris MB, Djeu JY (1991). Production of granulocyte-macrophage colony-stimulating factor by large granular lymphocytes stimulated with Candida albicans: role in activation of human neutrophil function. Blood 77:2259–2265.
Brandtzaeg P, Gabrielsen TO, Dale I, Muller F, Steinbakk M, Fagerhol MK (1995). The leucocyte protein L1 (calprotectin): a putative nonspecific defence factor at epithelial surfaces. Adv Exp Med Biol 371(A):201–206.
Braun BR, Johnson AD (1997). Control of filament formation in Candida albicans by the transcriptional repressor TUP1. Science 277:105–109.
Brettle RP (1997). Bacterial infections in HIV: the extent and nature of the problem. Int J STD AIDS 8:5–15.
Challacombe SJ (1994). Immunologic aspects of oral candidiasis. Oral Surg Oral Med Oral Pathol 78:202–210.[ISI][Medline]
Clemons KV, Stevens DA (2001). Overview of host defense mechanisms in systemic mycoses and the basis for immunotherapy. Semin Respir Infect 16:60–66.[Medline]
Coffey MJ, Phare SM, George S, Peters-Golden M, Kazanjian PH (1998). Granulocyte colony-stimulating factor administration to HIV-infected subjects augments reduced leukotriene synthesis and anticryptococcal activity in neutrophils. J Clin Invest 102:663–670.[ISI][Medline]
Colon MD, Toledo N, Valiente CL, Rodriguez N, Yano N, Mathews H, et al. (1998). Anti-fungal and cytokine producing activities of CD8+ T lymphocytes from HIV-1 infected individuals. Bol Asoc Med PR 90:21–26.
Coogan MM, Sweet SP, Challacombe SJ (1994). Immunoglobulin A (IgA), IgA1, and IgA2 antibodies to Candida albicans in whole and parotid saliva in human immunodeficiency virus infection and AIDS. Infect Immun 62:892–896.
Cox DT, Allen CM, Plouffe JF (1996). Locally invasive oral candidiasis mimicking zygomycosis in a patient with diabetic ketoacidosis. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 81:70–73.[ISI][Medline]
Csato M, Kenderessy AS, Judak R, Dobozy A (1990). Inflammatory mediators are involved in the Candida albicans killing activity of human epidermal cells. Arch Dermatol Res 282:348–350.[ISI][Medline]
Dale BA, Kimball JR, Krisanaprakornkit S, Roberts F, Robinovitch M, O’Neal R, et al. (2001). Localized antimicrobial peptide expression in human gingiva. J Periodontal Res 36:285–294.[ISI][Medline]
Deslauriers N, Coulombe C, Carré B, Goulet JP (1995). Topical application of a corticosteroid destabilizes the host-parasite relationship in an experimental model of the oral carrier state of Candida albicans. FEMS Immunol Med Microbiol 11:45–55.[ISI][Medline]
Deslauriers N, Cote L, Montplaisir S, de Repentigny L (1997). Oral carriage of Candida albicans in murine AIDS. Infect Immun 65:661–667.[Abstract]
Dieterich C, Schandar M, Noll M, Johannes FJ, Brunner H, Graeve T, et al. (2002). In vitro reconstructed human epithelia reveal contributions of Candida albicans EFG1 and CPH1 to adhesion and invasion. Microbiology 148:497–506.
Dinarello CA (1997). Interleukin-1. Cytokine Growth Factor Rev 8:253–265.[Medline]
Djeu JY, Blanchard DK (1987). Regulation of human polymorphonuclear neutrophil (PMN) activity against Candida albicans by large granular lymphocytes via release of a PMN-activating factor. J Immunol 139:2761–2767.[Abstract]
Dongari-Bagtzoglou A, Kashleva H (2003a). Candida albicans triggers interleukin-8 secretion by oral epithelial cells. Microb Pathog 34:169–177.[ISI][Medline]
Dongari-Bagtzoglou A, Kashleva H (2003b). Granulocyte-macrophage colony-stimulating factor responses of oral epithelial cells to Candida albicans. Oral Microbiol Immunol 18:165–170.[ISI][Medline]
Dongari-Bagtzoglou A, Wen K, Lamster IB (1999). Candida albicans triggers IL-6 and IL-8 responses by oral fibroblasts in vitro. Oral Microbiol Immunol 14:364–370.[ISI][Medline]
Dongari-Bagtzoglou A, Kashleva H, Villar CC (2004). Bioactive interleukin-1 is cytolytically released from Candida albicans-infected oral epithelial cells. Med Mycol 42:531–541.[ISI][Medline]
Dongari-Bagtzoglou A, Kashleva H, Villar CC (2005). Oral epithelial cells activate neutrophil antifungal activities in vitro. Med Mycol (in press).
Drobacheff C, Millon L, Monod M, Piarroux R, Robinet E, Laurent R, et al. (2001). Increased serum and salivary immunoglobulins against Candida albicans in HIV-infected patients with oral candidiasis. Clin Chem Lab Med 39:519–526.[ISI][Medline]
Elahi S, Pang G, Clancy R, Ashman RB (2000). Cellular and cytokine correlates of mucosal protection in murine model of oral candidiasis. Infect Immun 68:5771–5777.
Ellis M, Gupta S, Galant S, Hakim S, VandenVen C, Toy C, et al. (1988). Impaired neutrophil function in patients with AIDS or AIDS-related complex: a comprehensive evaluation. J Infect Dis 158:1268–1275.[ISI][Medline]
Epstein JB, Kimura LH, Menard TW, Truelove EL, Pearsall NN (1982). Effects of specific antibodies on the interaction between the fungus Candida albicans and human oral mucosa. Arch Oral Biol 27:469–474.[ISI][Medline]
Epstein JB, Hancock PJ, Nantel S (2003). Oral candidiasis in hematopoietic cell transplantation patients: an outcome-based analysis. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 96:154–163.[ISI][Medline]
Eversole LR, Reichart PA, Ficarra G, Schmidt-Westhausen A, Romagnoli P, Pimpinelli N (1997). Oral keratinocyte immune responses in HIV-associated candidiasis. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 84:372–380.[ISI][Medline]
Farah CS, Elahi S, Pang G, Gotjamanos T, Seymour GJ, Clancy RL, et al. (2001). T cells augment monocyte and neutrophil function in host resistance against oropharyngeal candidiasis. Infect Immun 69:6110–6118.
Farah CS, Elahi S, Drysdale K, Pang G, Gotjamanos T, Seymour GJ, et al. (2002a). Primary role for CD4(+) T lymphocytes in recovery from oropharyngeal candidiasis. Infect Immun 70:724–731.
Farah CS, Gotjamanos T, Seymour GJ, Ashman RB (2002b). Cytokines in the oral mucosa of mice infected with Candida albicans. Oral Microbiol Immunol 17:375–378.[ISI][Medline]
Fidel PL Jr (2002a). Distinct protective host defenses against oral and vaginal candidiasis. Med Mycol 40:359–375.[ISI][Medline]
Fidel PL Jr (2002b). The protective immune response against vaginal candidiasis: lessons learned from clinical studies and animal models. Int Rev Immunol 21:515–548.[Medline]
Fidel PL Jr (2004). History and new insights into host defense against vaginal candidiasis. Trends Microbiol 12:220–227.[ISI][Medline]
