Mucins (MUC5AC and MUC2) in Human Gastric Carcinomas Immunohistochemical Study of the Expression of MUC6 Mucin and Co-expression of Other Secreted
BACKGROUND & AIMS Among the human mucin complementary DNAs thus far identified, two (MUC5AC and MUC6) were cloned from stomach libraries. This study examines the distribution of MUC6 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 MUC6 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 MUC6 glycosylation. Using both immunohistochemical assays and in situ hybridization on stomach tissue sections, MUC6 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 MUC6 has a distinct tissue distribution pattern, different from that of MUC1-MUC5; MUC5AC and MUC6 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.