Expression of common cytoplasmic antigens by epithelial cells of thymus and epidermis

The expression of common cytoplasmic antigens by thymic epithelial cells and keratinocytes was analyzed by immunolabelling on cryostat sections of human and animal thymus and epidermis. Experimental sera to human epidermal keratin subunits of molecular weight (MW) 67 K, 63 K and 55 K were used, as well as human sera with antibodies to epidermal cytoplasmic antigens (KCA), reacting either with U-Cyt antigens expressed by cells from the upper compartment of the epidermis or with BLC antigens in cells from the basal layer. It was demonstrated that keratin subunits of MW 67 K and 63 K were detected only in the upper layers of human epidermis, whereas 55 K was present in all epidermal layers. On rabbit lip a labelling was obtained throughout the epidermis by the three immune sera. On thymus sections a cytoplasmic staining of epithelial cells was observed with the three immune sera, suggesting an antigenic similarity between cytokeratins of thymus epithelial cells and keratins of the upper layers of human epidermis. Two human sera with U-Cyt antibodies and one with BCL antibodies labelled human thymic epithelial cells but were negative with mice thymus. Ten other sera with KCA were negative on both thymus. These results show that the expression of keratins and cytoplasmic antigens, defined by human KCA, differed in immunofluorescence on normal human epidermis, rabbit lip and thymic epithelial cells. These suggests a heterogeneity among human keratinocyte cytoplasmic antigens defined by KCA and the presence in man of common antigenic constituents from keratins in epidermal cells and thymic epithelial cells.