The CD43 130-kD peripheral T-cell activation antigen is downregulated in thymic positive selection.

Specific glycoforms of CD43, the major O-glycosylated cell-surface protein on T lymphocytes, can affect cell adhesion according to the types of carbohydrate side chains carried. In the peripheral immune system, CD43 130 kD, which carries core 2 O-glycan structures on its surface, is an activation antigen expressed on both CD4 and CD8 single-positive (SP) T cells. We have previously shown that the 115-kD resting and 130-kD activation glycoforms of murine CD43 are differentially regulated on peripheral SP T cells. In this study, we used transgenic mice expressing T-cell receptors (TCRs) specific for antigens presented by class I and class II major histocompatibility complex (MHC) molecules to determine whether CD43 glycoforms are involved in thymocyte differentiation. Positive selection in these mice results in an increase in the production of CD8 and CD4 SP T cells, respectively, which express the transgenic TCR. Positive selection is also accompanied by the upregulation of TCR, CD69, and CD5. Using these markers to define stages of thymocyte maturation, we found that CD43 130 kD was downregulated in the positive selection of CD4 CD8 double-positive thymocytes expressing a class I but not class II MHC-restricted TCR. These data suggest that core 2 glycosyltransferase (C2GnT) modulated expression of CD43 glycoforms may be involved in thymic selection events.