Effector Cells in Allelic

The effector cell mechanisms involved in allograft or tumor rejection are still controversial (1) . Sprent et al . (2) recently demonstrated that injection of Lyt-2' cells (positively purified by the panning method) into adult, thymectomized, bone marrow-reconstituted (ATXBM)' B6 mice resulted in rejection of skin from the H-2Kb mutant strain of B6.C-H-2bm' (bmI), but not the H-21Ab mutant strain of B6 .C-H-2bm'2 (bm12), whereas injection of L3T4' cells into these mice resulted in rejection of skin from bm 12, but not bm 1 mice . Similarly, Rosenberg et al . (3) reported that bmI skin grafts were rejected by B10 nude mice reconstituted with B6 spleen cells depleted of L3T4 cells, but not of Lyt-2' cells by pretreatment with mAb and complement. These studies suggested that the rejections of skin grafts differing at H-2 class I and class II loci are mediated by Lyt-2' and L3T4' T cells, respectively . Although there have been several studies on B6 H2b mutant strains by investigating the immune responsiveness of B6 mice against them, there have been few on the cellular mechanisms of the immune responses against allelic MHC class I or II antigens . Previously, we and others demonstrated that injections of anti-Lyt-2 and antiL3T4 mAb into mice caused selective depletions of Lyt-2' and L3T4+ cells, respectively (4-7) . In this study we investigated the effect of in vivo administration of anti-Lyt-2 .2 mAb, anti-L3T4 mAb, or both to recipient mice on skin graft survival and found that, besides Lyt-2' effector cells, L3T4' cells can also mediate skin graft rejection with allelic H-2 class I differences in two different ways, depending on the strain combination .