COEXPRESSION OF IL-2 RECEPTOR P55 AND P75 BY CIRCULATING BLOOD-LYMPHOCYTES

By using high-sensitivity fluorescence and flow cytometry, it is possi ble to show that 30-40% of lymphocytes from PBL express the p55 chain of the IL-2 receptor, whereas the p75 chain is expressed at low concen trations on most lymphocytes without in vitro activation. The availabi lity of a second fluorochrome capable of high sensitivity allows simul taneous analysis of p55 and p75, albeit with some sacrifice in sensiti vity. Two-color analysis shows that a small proportion of cells (1-6%) coexpress measurable concentrations of both chains of the IL-2 recept or, and three-color studies show that these cells are predominantly CD 4-positive T cells and express the CD45R0 isoform of the leucocyte-com mon antigen, i.e., have the phenotype of activated helper T cells. The se cells may be a useful indicator of immune activation.