Mucins as key molecules for the classification of intestinal metaplasia of the stomach

Mucins and mucin-associated carbohydrates have a distinct expression pattern that can be modified under pathological conditions. Normal gastric mucosa expresses MUC1 and MUC5AC in foveolar epithelium and MUC6 in the glands. Lewis type-1 chain antigens (Le(a) and Le(b)) are expressed in foveolar epithelium, whereas Lewis type-2 chain antigens (Le(x) and Le(y)) are expressed in the glands. In this study we used monoclonal antibodies to evaluate the pattern of mucins and Lewis type-1 carbohydrates in intestinal metaplasia (IM) and compared it with IM types determined using histochemistry. In type-I or complete IM we found expression of MUC2 intestinal mucin and decreased/absent expression of MUC1, MUC5AC and MUC6. In type-II/III or incomplete IM there was co-expression of MUC2 and the mucins expressed in the stomach. No major differences were detected among the three IM types regarding expression of Lewis antigens. Furthermore we observed that sialylated compounds other than sialyl-Le(a) are responsible for histochemical detection of sialomucins and that sulpho-Le(a/c) is expressed in the presence or absence of sulphomucins detected using histochemistry. We conclude that mucin immunohistochemistry may replace classic histochemistry for the classification of IM into complete and incomplete types. The present study challenges the distinction of type-II from type-III IM since we did not observe major differences in the expression profile of mucins and Lewis type-1 carbohydrates. Finally, it seems necessary to evaluate the predictive value of IM according to the presence of specific sulphated carbohydrates (e.g. sulpho-Le(a/c)) rather than histochemically detected sulphomucins.