CD4(-CELLS ARE ABLE TO REJECT CLASS-I DISPARATE ALLOGRAFTS() T)

The ability of CD4(+) T cells to reject class I mismatched skin allogr afts remains controversial. In this study, we compare the ability of C D4(+) T cells to reject class I disparate skin grafts differing by eit her a single class I allelic disparity or only 3 amino acids encoded b y the H-2K locus. We demonstrate that skin grafts across a full H-2K a llelic disparity, but not across a disparity of only three amino acids are efficiently rejected by CD4(+) T cells. This observation is consi stent with the possibility that peptides derived from allogeneic class I molecules generated through the major histocompatibility complex (M HC) class II antigen processing pathway can be recognized by host CD4 T cells and lead to rejection of class I mismatched skin grafts. The a vailability of peptides derived from allogeneic MHC class I molecules for presentation by host MHC class II may determine the efficiency of rejection of class I mismatched allografts by CD4(+) T cells. Thus, cl ass I mismatched allografts can be rejected by CD4(+) T cells provided that host and donor MHC class I molecules are sufficiently disparate to activate CD4(+) effectors.