Histo-blood group antigens in human fetal thymus and in thymomas.

The glycosylation of epithelial cell surface antigens follows cellular differentiation, and changes in the pattern of expression are seen in various premalignant and malignant epithelial lesions. The distribution of type-2 chain ABH-carbohydrate structures (N-acetyl-lactosamine, H-type 2 chain, Le-y, Le-x and sialyl-Le-x) of the ABO-histo-blood group system was investigated in 19 normal fetal thymuses (gestational age 16 to 39 weeks) and in 19 thymomas in order to study possible tumor-associated changes in the glycosylation pattern. The material was investigated by immunochemical stainings of formalin-fixed paraffin-imbedded tissue using monoclonal antibodies with defined specificity. In fetal thymus the epithelial cells of the medulla and the Hassal's bodies strongly expressed elongated carbohydrate structures (Le-y, Le-x and sialyl-Le-x). In a few cases the cortical epithelial cells weakly expressed Le-x and sialyl-Le-x. Compared with fetal thymus 16 of the thymomas showed a total loss, or a very much reduced expression of elongated carbohydrate structures. Three thymomas, which histologically had been reclassified according to Kirchner & Müller-Hermelink (14) as high grade thymic carcinomas, revealed strong expression of Le-y, moderate expression of Le-x and weak expression of sialyl-Le-x. This is of interest as in other tumors Le-y is correlated with increased cell motility and with poor prognosis.