ACTIVATION ANTIGEN EXPRESSION ON HUMAN T-CELLS .1. ANALYSIS BY 2-COLOR FLOW-CYTOMETRY OF UMBILICAL-CORD BLOOD, ADULT-BLOOD AND LYMPHOID-TISSUE

Activation antigens (actags) were detected on T cells at low levels of intensity by carefully defining negative cells with a panel of contro l antibodies. The mean percentage of blood T cells from healthy volunt eers that expressed actags were 22% (CD25), 54% (CD26), 38% (CD38%), 1 2% (CD54), 6% (CD69) and 21% (HLA-DR). The variability of actag expres sion detected by this sensitive method was determined on healthy volun teers by repeated estimation over a year. The percentage of T cells ex pressing CD25 and CD26 varied no more than repeated estimation of the CD4 T cell subset, whereas other actags showed greater variability. Th e antigen density of these actags on T cells was determined in relatio n to CD4 antigen density, and for most actags ranged from 10% to 75% o f the level of CD4 antigen density except for CD7 and HLA-DR, which co uld exceed that of CD4. Different degrees of actag expression characte rized T cells from different blood and lymphoid tissues. CD26, CD38 an d CD45RA were universally expressed in ford blood at higher antigen de nsity than adult blood. This immature pattern was consistent with rece nt thymic emigration. CD25, CD45RO, CD54 and HLA-DR progressively incr eased from cord blood through adult blood to lymphoid tissues, consist ent with antigen-driven activation, whereas CD26 and CD45RA decreased. CD69, a very early activation antigen, abruptly increased in lymphoid tissue, exceeding CD25 by two-to-three-fold and suggesting a pre-acti vation state that may not involve commitment to antigen-driven prolife ration. CD7 and CD38 expression was higher in cord blood and lymphoid tissue than in adult blood, indicating both an antigen-independent and -dependent up-regulation.