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 identified, two (MUC5AC and MUCG) were cloned from stomach libraries. This study examines the distribution of MUCG in normal tissues and compares it with that of MUC5AC as well as with the expression of Lewis blood group antigens. Methods: Affinity-purified rabbit antibodies detecting epitopes within the repetitive sequence of MUC5AC and MUCG were used in enzyme-linked immunosorbent assays and immunohistochemical assays. RNA expression was analyzed by in situ hybridization. Double-labeling immunofluorescence was used to study apomucin and Lewis antigen coexpression. Results: MUC6 is detected in the stomach, colon, gallbladder, and endocervix. Two patterns of staining are observed, perinuclear and diffuse cytoplasmic, possibly reflecting differences in MUCG glycosylation. Using both immunohistochemical assays and in situ hybridization on stomach tissue sections, MUCG is expressed mainly in antral mucous cells, whereas MUC5AC is detected mainly in the superficial epithelium and neck glands. In antral mucosa, MUC6+ cells express Lewis(y), whereas MUC5AC+ cells express Lewis(b) and sialyl-Lewis(a). Conclusions: It was concluded that MUCG has a distinct tissue distribution pattern, different from that of MUC1-MUC5; MUC5AC and MUCG are expressed by different cellular populations in normal stomach; and in this tissue, MUC5AC+ cells and MUC6+ cells show different patterns of Lewis antigen expression.