[A study on T cell subsets responsible for syngeneic mixed lymphocyte reaction].

In vitro proliferation of T cells in response to the stimulation with syngeneic non-T cells has been regarded as the syngeneic mixed lymphocyte reaction (SMLR). SMLR has been considered to represent a characteristic of immunological response to the self antigen. It was demonstrated that the T cell subset proliferating in the SMLR belonged to CD4+ T cell population and was characterized as CD45RA+ memory Th cell subset. It has been postulated that CD8+ T cells are not significantly involved in the SMLR. In the present study, SMLR was analyzed with nylon-wool-purified splenic T cells as responders and splenic dendritic cells (DC) as stimulators. With the use of carboxyfluorescein diacetate succinimidyl ester (CFSE), it was demonstrated that the predominant proliferating subset was CD8+ T cell 3 days after the culture. However, when CD4+ T cells were depleted before SMLR, CD8+ T cells hardly proliferated. From the analysis of several activation markers, the proportion of the activated T cells was higher in the CD8+ T cells than in CD4+ T cells. For further elucidation of T cell subsets responsible for SMLR, responder cells which expressed CD62L, a marker for naive T cells, were examined. When CD62L+ and CD62L- T cells were cultured with DC, CD62L+ T cells generated vigorous proliferation, whereas CD62L- T cells showed quite low response. The present findings demonstrate that CD8+ T cells and/or CD62L+ T cells play certain roles in SMLR.