CD45RA-expressing memory/effector Th cells committed to production of interferon-gamma lack expression of CD31

It has been considered before that human naive and memory/effector CD4(+) T-cells cannot be subdivided solely according to the differential expression of CD45 isoforms. By the lack of expression of CD31 we have identified a subset of CD4(+) CD45RA(+) CD31(-) cells which show distinct features of antigen-experienced Th1 cells. Short term stimulation of highly purified human peripheral blood CD4(+) T-cells with PMA/ionomycin, followed by the cytometric analysis of intracellular cytokines, showed that a minor subpopulation of CD4(+) CD45RA(+) CD45RO(-) cells is able to produce interferon-gamma (IFN-gamma) rapidly, a characteristic of antigen-experienced Th1 cells. Whereas among CD45RA(+) CD4(+) T-cells both CD31(+) and CD31(-) subsets produce interleukin-2 (IL-2) upon PMA/ionomycin stimulation, only the CD31(-) subpopulation is able to produce IFN-gamma. Thus, our phenotypic and functional characterization of CD45RA(+) CD45RO(-) Th cells shows that CD45RA(+) CD45RO(-) cells do not represent a homogeneous population of antigen-unexperienced, naive T-cells. We speculate that a certain subset of human CD4(+), CD45RO(+) memory T-cells reverts to expression of the CD45RA isoform, and that this subset can be identified by the lack of CD31 expression. (C) 1997 Elsevier Science B.V.