Figure 3. Blood group AB patient. (A) A antigen staining is strong in normal epithelium (Nor), but absent in dysplastic (Dys) and in tumor (Tum) tissue. (B,C) Antigen B staining is weak in normal, but positive in dysplastic epithelium. (D) Three-day wound stained with antibodies to blood-group antigen A precursor (Le^y). The outgrowth of the epithelium shows loss of A and B antigens and up-regulation of the precursor Le^y (see also Fig. 5). (E,F) Oral carcinoma from a blood-group AO person. A antigen staining is positive in a part of the tumor (E) and in normal epithelium (not shown), but negative in the remaining part of the tumor (F). (G) Agarose gel of the ABO gene-specific products in the above AO person. Lanes 1, 4, 7, and 10 show undigested PCR products; lanes 2, 5, 8, and 11 show Kpn I digested, revealing O allele; lanes 3, 6, 9, and 12 show BstE II digested, revealing A allele. Blood-group type O control and a negative control are included. In the normal epithelium, both A and O alleles are present; the positive-stained tumor (Tumor+) shows O allele loss, whereas the negative-stained tumor (Tumor-) shows A allele loss.