REJUVENATED EXPRESSION OF H-2K(B) IN RMA-S CELLS DOES NOT AFFECT ALLOREACTIVE T-CELL-MEDIATED AND NATURAL-KILLER CELL-MEDIATED LYSIS

Reduced sensitivity to alloreactive cytotoxic lymphocytes (CTLs) and i ncreased susceptibility to natural killer (NK) cells in vivo and in vi tro are two phenotypic characteristics that have been attributed to th e reduced major histocompatibility complex (MHC) ligand density on the surface of an antigen-presentation-defective cell line, RMA-S. As RMA -S exhibits both defective processing of antigenic peptides and very l ow class I expression, it is uncertain which is responsible for the ab ove characteristics. In this report, we show that the phenotype cannot be reversed by increasing the number of K(b) + beta2-M complexes expr essed on the cell surface. These findings emphasize the importance of association of MHC class I molecules with endogenously processed pepti des for biological interaction with alloreactive CTLs and NK cells.