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CONCISE REVIEW |
1 Department of Oral and Maxillofacial Surgery, Oral Biochemistry Laboratory and Salivary Clinic, Rambam Medical Center, and Faculty of Medicine, Technion-Israel Institute of Technology, Haifa, Israel; and
2 Department of Bone Marrow Transplantation, Chaim Sheba Medical Center, Tel Hashomer, Israel;
* corresponding author, nagler{at}tx.technion.ac.il
| ABSTRACT |
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KEY WORDS: graft vs. host disease saliva salivary gland sialochemistry sialometry
| INTRODUCTION |
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Chronic GVHD may develop as an extension of acute GVHD (progressive onset), after resolution of acute GVHD (quiescent onset), or without preceding acute GVHD (de novo onset). Chronic GVHD is categorized as either limited (localized skin and/or hepatic involvement) or extensive (diffuse skin and/or multi-organ involvement); the latter is associated with a worse prognosis (Sullivan et al., 1981). The introduction of low-intensity conditioning (LIC) and non-myeloablative alloSCT did not result in reduction in the frequencies of cGVHD; in fact, it seems that the frequencies are even increasing (Shimoni and Nagler, 2001). cGVHD usually develops more than 100 days after transplants, with a tendency for later occurrence in patients receiving peripheral blood stem cell grafts and patients undergoing LIC alloSCT (Shimoni and Nagler, 2001; Schmitz et al., 2002). Chronic GVHD typically resembles a connective-tissue-autoimmune-like immunological disorder, characterized by lichenoid or sclerodermoid lesions of skin along with joint contractors similar to those seen in systemic sclerosis. The clinical and pathologic features resemble the overlapping of several collagen vascular diseases and immune dysregulation with eosinophilia, circulating autoantibodies, hypergammaglobulinemia, and plasmacytosis of the viscera and lymph nodes (Sullivan et al., 1981). The skin changes that are the hallmark of the disease include papulosquamous dermatitis, plaques, desquamation, dyspigmentation, and vitiligo. Chronic GVHD has histopathological features similar to those of SSc, manifested predominantly by sclerosis of the thickened reticular dermis due to the increased synthesis of collagen (Shulman et al., 1978). The histologic distinction between the papillary and reticular dermis may not be apparent because of sclerosis. Cutaneous appendages become encased in collagen and tend to disappear. There is variable perivascular and interstitial inflammatory cell infiltrate, composed predominantly of lymphocytes and occasionally plasma cells (Janin-Mercier et al., 1984). Less frequent skin findings include poikiloderma, reticulated hyperpigmentation, alopecia, dystrophic nails, leucoderma bullae, discoid lupus erythematosis, and photosensitivity. The pathophysiologic mechanism involves autoreactive lymphocytes and cytokine dysregulation (Ilan et al., 2000; Nagler et al., 2000).
Current therapeutic options are limited. Less than 20% of patients with untreated extensive cGVHD survive with Karnofsky performance scores
70% (Sullivan et al., 1981). Currently, corticosteroids alone or in combination with cyclosporin remain the treatment of choice for established cGVHD. Although such conventional therapy has achieved complete responses in approximately 50% of patients, the disease remains barely controllable in most patients. Other therapeutic options that have been tried over the years include compounds like thalidomide, mycophenolate mofetil, tacrolimus, rapamycin, clofazimine, etretinate, hydroxycloroquine, ursodeoxycholic acid, penicillamine, cyclophenile, and nedocromil sodium as well as medical procedures such as induction of oral tolerance, total lymphoid irradiation, phototherapy (PUVA), and extracorporeal phototherapy (Gaziev et al., 2000).
| PATHOGENESIS RELATED TO SALIVARY GLANDS |
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| SIALOMETRIC ANALYSIS |
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| SIALOCHEMICAL ANALYSIS |
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The reported three- to four-fold increase in Na concentration (Nagler and Nagler, 2001) is in agreement with reports from two other fundamental studies in which Izutsu et al. (1983a,b) demonstrated an increase in Na concentrations in the secretions of both minor salivary glands and whole saliva of GVHD patients. This increase in Na concentration could be accounted for by GVHD-induced and lymphocyte-infiltration-mediated damage to the Na-re-absorbing salivary ductal system. A similar salivary Na increase was demonstrated in Sjögrens syndrome patients as well, and the etiology suggested in this autoimmune disease was similar, being also based on the role played by infiltrating autoreactive lymphocytes (Chisholm and Mason, 1968). Concentrations of the three other electrolytesK, Ca, and Pwere found to be similar in patients and in controls (Nagler and Nagler, 2001). This result is also supported by Izutsu et al.(1983a), who reported that resting salivary K concentrations in GVHD patients are not different from those in controls.
With respect to the anti-infection activity and the maintenance of mucosal integrity in the oral cavity, it should be emphasized that salivary IgA and EGF are of major importance (Deville de Périère and Aranciba, 198889; Marti et al., 1989). The significant salivary IgG increase in GVHD patients is also in accord with the previously mentioned study by Izutsu et al.(1983a). The significant elevation of EGF, total protein, albumin, and IgG could result from direct GVHD-induced damage to the salivary parenchyma, as previously suggested. However, it could also result from a transudation of serum components across the damaged and inflamed oral epithelium and gingiva, which are sites affected by the disease (Nagler et al., 1996a). Thus, it may be concluded that a multi-site mechanism may be differentially responsible for the observed increase of various components which either are being secreted from the salivary glands as EGF or leak from the serum into the saliva as albumin. The salivary EGF is of special importance, and more so at resting conditions, since resting salivary secretion is the dominant condition during most of the day and night, and the dominant secreting salivary gland in this condition is the submandibular gland (Nagler and Nagler, 1999). In any event, a mere "concentrating effect" of reduced secreted volume due to a decrease of the watery component of the saliva (related to a specific insult of the muscarinic signal transduction pathway, for example) is excluded, since such a mechanism might explain an identical increase of the EGF, total protein, and immunoglobulins but not a differentiated one, as observed.
| MOLECULAR ASPECTS OF GVHD AND THEIR SALIVARY IMPLICATIONS |
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Another new approach illustrating and emphasizing the role of cytokines in GVHD is cytokine gene polymorphism, which is associated with functional differences in cytokine regulation. A correlation was found between the severity and frequency of GVHD and IFN-alpha, IL-6, IL-10, and TNF-alpha gene polymorphism. Specifically, patients homozygous for the IFN-alpha Intron allele 3 had more severe (Grade III-IV) acute GVHD. Similarly, patients possessing the IL-6 (-174) G allele had a trend toward higher grades of acute GVHD, and those homozygous for the IL-6 (-174) G allele were more likely to develop chronic GVHD (Cavet et al., 2001).
Recently, the rather new cytokine IL-18 has been implicated in GVHD (Panoskaltsis-Mortari et al., 2000; Itoi et al., 2001). Increased serum levels of IL-18 were found in patients who developed GVHD post-allogeneic PBSCT. IL-18 is a cytokine with wide-ranging biological functions, including not only innate but also acquired immunity, including both Th responses, particularly in collaboration with IL-12, and Th2 responses. IL-18 is involved in the development of cytotoxic T-lymphocytes and natural killer cells, which may mediate the salivary injury observed in GVHD. Regarding the mechanism, in murine experiments, it was demonstrated that recipient mice transplanted with H-2 disparate donor GLD/GLD spleen cells, which lack functional Fas ligand (FasL), developed GVHD, but no elevation of IL-18 was observed (Panoskaltsis-Mortari et al., 2000), indicating that FasL mediates IL-18 release in GVHD. Furthermore, IL-18 elevation was found to be derived from host cells in a caspase-1-dependent manner (Panoskaltsis-Mortari et al., 2000).
Salivary-mediated lesions in GVHD show histological features of cell death with lymphocyte infiltration. It was recently demonstrated that perforin and granzyme B are involved in the process of apoptosis, induced by cytotoxic T-lymphocytes, which leads to epidermal injury in GVDH (Higaki et al., 2001). There may be a similar mechanism at work in the salivary injury in GVHD.
Interleukin-13 is a new Th2 cytokine that has recently been shown to suppress alloreactivity and to be of protective value in GVDH. Moreover, the keratinocyte growth factor (KGF) that has been demonstrated in both mice and humans as ameliorating GVHD may operate through IL-13/KGF (Panoskaltsis-Mortari et al., 2000), and IL-13 may therefore be of therapeutic value in ameliorating GVHD-mediated salivary injuries. One of the mechanisms that may be critical to the attraction and recruitment of cytotoxic T-cells to the salivary glands, thus mediating the GVHD-mediated injury, is the production of macrophage inflammatory protein 1 alpha (MIP-1 alpha), since it was recently shown that production of MIP-1 alpha by donor T-cells is important in the occurrence of GVHD and functions in a tissue-dependent fashion (Serody et al., 2000).
Another factor that may be implicated in salivary injury is HSP 70. It has been shown that increased levels of HSP 70 and antibodies reactive with HSP 70 parallel the onset and severity of GVHD. Moreover, deoxyspergualin, which ameliorates GVHD, has been shown to reduce hsp 70 levels, resulting in diminished serum levels of IL-2, IFN-gamma, and TNF-alpha, which have been implicated in GVHD-mediated end-organ injury (Goral et al., 2000).
A molecule that has been implicated in the tissue destruction of GVHD is nitric oxide. Increased levels of nitric oxide have been shown in GVHD, and blockage of nitric oxide production and pathways may have a therapeutic role. The onset of GVHD is accompanied by macrophage (M phi) priming, which results in expression of nitric oxide synthase and the production of nitric oxide in response to LPS. Continuous exposure to IFN-gamma is required to maintain a primed state of M phi during GVHD. Indeed, increased IFN-gamma in RNA has been demonstrated in salivary gland tissue in mice with GVHD (Kichian et al., 1996).
| MECHANISM OF SALIVARY INVOLVEMENT IN GVHD |
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Accordingly, a suggested pathogenesis mechanism for salivary gland involvement in GVHD is composed of the following: HLA up-regulation, mononuclear infiltration, and cytokine dysregulation (Izutsu et al., 1983a; Chaushu et al., 1994a). Indeed, various cytokinesincluding IL-2, IL-6, IFN-
, TNF-
, and IGFhave recently been shown to influence salivary cell function and survival and the production of salivary immunoglobulin and/or saliva (Marmary et al., 1994; Nagler et al., 1997). Therefore, it is possible that a massive lymphocytic infiltration and aberrant production of cytokines are responsible for the described GVHD-induced salivary effects. This leads to gland destruction and hypofunction and causes severe xerostomia, which also contributes to the oral manifestations observed in GVHD patients, since various salivary protective characteristics are lost (Sullivan et al., 1981). Furthermore, the deleterious effect of hyposalivation is exacerbated by an altered salivary composition. It is important to note that the major salivary immunoglobulin related to protecting both soft and hard tissues, secretory IgA, was reported by Izutsu et al. (1983a, 1987) to be significantly reduced in GVHD patients. In their 1987 paper, it was stated that the macromolecule content of minor salivary glands is significantly different from that of major salivary glands. That may explain the presumably contradictory finding of increased salivary immunoglobulin levels in whole saliva of GVHD patients which was reported recently (Nagler and Nagler, 2001). In any case, this increase in the concentrations of the other salivary protecting "players"total IgA, IgG, and EGFmay actually be reduced in total quantity in the oral cavity because of the overwhelming reduction in salivary volume. Moreover, because of the increased viscosity of the saliva, they may not be available at the required mucosal sites where damage occurs but remain ineffective within the saliva itself. Accordingly, the epithelial barriers, which are already severely damaged in GVHD, are left with significantly compromised protection. In any case, it is still controversial whether the relatively low dose of radiotherapy administered prior to bone marrow transplantation is not responsible for the observed salivary gland, as was shown in an animal model (Nagler et al., 1996b). In contrast, Brattström et al.(1991) reported that, in humans exposed to total body irradiation of 7.5 Gy and above prior to bone marrow transplantation, the salivary glands were profoundly affected. This was demonstrated by an increase of the serum amylase levels from a mean of 3.2 mukat/L prior to irradiation to a mean of 100.3 mukat/L on the day following irradiation, while 90% of this increase originated from salivary isoamylase.
In summary, the suggested multisite mechanism gains support from the following:
As for the presumed resemblance of salivary gland involvement in GVHD and in Sjögrens syndrome, it is important to note the finding of Hiroki et al.(1996), who found two examined parameters to be different in these diseases:
Although it is tempting to assume that both entities are very similar in light of the immunological background and the mutual clinical symptoms of xerostomia and xerophthalmia, one should question this assumption.
| FUTURE DIRECTIONS |
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| ACKNOWLEDGMENTS |
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Received December 27, 2001; Last revision September 15, 2003; Accepted November 14, 2003
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