REGULATION OF ADHESION MOLECULE EXPRESSION BY CD8 T-CELLS IN-VIVO .2.EXPRESSION OF L-SELECTIN (CD62L) BY MEMORY CYTOLYTIC T-CELLS RESPONDING TO MINOR HISTOCOMPATIBILITY ANTIGENS

Activation of murine T cells by Ag or mitogens results in changes in t he expression of several cell-surface adhesion molecules that alter th e way in which these cells migrate and localize in tissues in vivo. As naive CD8 precursor cells in lymph nodes (LN) differentiate into effe ctor CTL in response to a skin allograft, they up-regulate their expre ssion of Pgp-1 (CD44), VLA-4, and LFA-1 (CD11a/18), while down-regulat ing L-selectin (CD62L). All cytolytic activity is therefore present in this minor population of L-selectin(-) Pgp-1(high) LN T cells. We now report that, late after rejection of minor histocompatibility Ag-disp arate skin grafts, the majority of memory CD8 T cells express both L-s electin and Pgp-1 and thus would be expected to migrate via the classi cal route of recirculation through LN. Furthermore, restimulation of t hese memory cells by Ag causes them to down-regulate L-selectin, so th at memory-effector cells have the same L-selectin(-) Pgp-1(high) pheno type as do primary effector cells. These results are in contrast to re cent reports that murine and ovine CD4 memory cells do not express L-s electin or recirculate through LN high endothelial venules. In additio n, although virgin and naive CD4 cells may be divided based upon their expression of CD45RA or CD45RB, memory CD8 cells cannot be differenti ated by their expression of CD45 isoforms.