Immunohistochemical study of the expression of MUC6 mucin and co-expression of other secreted mucins (MUC5AC and MUC2) in human gastric carcinomas

To investigate the expression of MUC6 mucin in gastric carcinomas, we gener ated a novel monoclonal antibody (MAb CLH5) using an MUC6 synthetic peptide . MAb CLH5 reacted exclusively with the MUC6 peptide and with native and de glycosylated mucin extracts from gastric tissues. MAb CLH5 immunoreactivity was observed in normal gastric mucosa restricted to pyloric glands of the antrum and mucopeptic cells of the neck zone of the body region. In a serie s of 104 gastric carcinomas, 31 (29.8%) were immunoreactive for MUC6. The e xpression of MUC6 was not associated with histomorphological type or with c linicopathological features of the carcinomas. Analysis of the co-expressio n of MUC6 with other secreted mucins(MUC5AC and MUC2) in 20 gastric carcino mas revealed that different mucin core proteins are co-expressed in 55% of the cases. MUC6 was co-expressed and co-localized with MUC5AC in 45% and wi th MUC2 in 5% of the cases. Expression of MUC2 alone was observed in 25% of the cases. All carcinomas expressing MUC2 mucin in more than 50% of the ce lls were of the mucinous type according to the WHO classification. The co-e xpression of mucins was independent of the histomorphological type and stag e of the tumors. In conclusion, we observed, using a novel well-characteriz ed MAb, that MUC6 is a good marker of mucopeptic cell differentiation and i s expressed in 30% of gastric carcinomas, independent of the clinicopatholo gical features of the cases. Furthermore, we found that co-expression and c o-localization of mucins in gastric carcinomas is independent of histomorph ology and staging. Finally, we observed that intestinal mucin MUC2 is expre ssed as the most prominent mucin of the mucins tested in mucinous-type gast ric carcinomas.