MUC6 APOMUCIN SHOWS A DISTINCT NORMAL TISSUE DISTRIBUTION THAT CORRELATES WITH LEWIS ANTIGEN EXPRESSION IN THE HUMAN STOMACH

Background & Aims: Among the human mucin complementary DNAs thus far i dentified, two (MUC5AC and MUCG) were cloned from stomach libraries. T his study examines the distribution of MUCG in normal tissues and comp ares it with that of MUC5AC as well as with the expression of Lewis bl ood group antigens. Methods: Affinity-purified rabbit antibodies detec ting epitopes within the repetitive sequence of MUC5AC and MUCG were u sed in enzyme-linked immunosorbent assays and immunohistochemical assa ys. RNA expression was analyzed by in situ hybridization. Double-label ing immunofluorescence was used to study apomucin and Lewis antigen co expression. Results: MUC6 is detected in the stomach, colon, gallbladd er, and endocervix. Two patterns of staining are observed, perinuclear and diffuse cytoplasmic, possibly reflecting differences in MUCG glyc osylation. Using both immunohistochemical assays and in situ hybridiza tion on stomach tissue sections, MUCG is expressed mainly in antral mu cous cells, whereas MUC5AC is detected mainly in the superficial epith elium and neck glands. In antral mucosa, MUC6+ cells express Lewis(y), whereas MUC5AC+ cells express Lewis(b) and sialyl-Lewis(a). Conclusio ns: It was concluded that MUCG has a distinct tissue distribution patt ern, different from that of MUC1-MUC5; MUC5AC and MUCG are expressed b y different cellular populations in normal stomach; and in this tissue , MUC5AC+ cells and MUC6+ cells show different patterns of Lewis antig en expression.