TEMPORAL LOSS OF THE ACTIVATED L-SELECTIN-LOW PHENOTYPE FOR VIRUS-SPECIFIC CD8(-CELLS() MEMORY T)

Whether the L-selectin-low (L-sel-lo) phenotype of acutely stimulated CD8(+) T cells is a permanent characteristic of long-term memory CTL p recursors (p) is addressed for mice primed with an influenza A virus o r the murine parainfluenza type 1 virus, Sendai virus. In both cases, many oi the splenic CD8(+) CTLp gradually lose the predominantly L-sel -lo profile associated with recently generated CTLp populations. The i nfluenza-specific CTLp also tend to revert from the activated alpha(4) -integrin-high to the resting alpha(4)-integrin-low form. The kinetics of the switch back to the ''naive'' L-sel-hi phenotype differs for th e influenza and Sendai virus models, perhaps reflecting events occurri ng during the acute phases of these responses. The return to being L-s el-hi is not due to irreversible lymphocyte senescence, because restim ulation of this set with the inducing virus in vitro causes most of th e cells to become L-sel-lo. Also, despite the time-related drift of th ese particular memory CTLp to the L-sel-hi state, the size of the tota l pool of L-sel-lo CD8(+) T cells increases with age.