UP-REGULATION OF SURFACE-MARKERS ON DYING THYMOCYTES

Using terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling (TUNEL) to detect cells undergoing early apoptosis, we have defined the surface markers expressed on CD4(+)CD8(+) thymocytes undergoing spontaneous or steroid-induced apoptosis in tissue culture. Some surface markers, e.g., CD4, CD8, and heat stable antigen, are downregulated on apoptotic thymocytes. Surprisingly, however, other markers are upregulated; this applies to T cell receptor beta/CD3, CD69, and CD25 expression. Upregulation of these markers is restricted to a discrete subset of apoptotic cells.