Circulating human T and B lymphocytes express the p55 interleukin-2 receptor molecule (TAC, CD25).

Using a highly sensitive immunofluorescence procedure 15-45% of blood lymphocytes from normal human donors can be shown to react with anti-TAC (CD25) monoclonal antibodies. The standard procedure for indirect immunofluorescence does not allow the detection of these CD25-positive cells. Ten healthy adults were tested, and all showed a population of positive cells. Three donors have been tested more than once, and have given consistent results. Three different CD25 antibodies were used, again with consistent results. Double-marker studies showed that the positive cells included B cells, as well as CD4-bearing and CD8-bearing T cells.