Rejuvenated expression of H-2Kb in RMA-S cells does not affect alloreactive T cell- and natural killer cell-mediated lysis.

Reduced sensitivity to alloreactive cytotoxic lymphocytes (CTLs) and increased susceptibility to natural killer (NK) cells in vivo and in vitro are two phenotypic characteristics that have been attributed to the 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 low class I expression, it is uncertain which is responsible for the above characteristics. In this report, we show that the phenotype cannot be reversed by increasing the number of Kb + beta 2-M complexes expressed on the cell surface. These findings emphasize the importance of association of MHC class I molecules with endogenously processed peptides for biological interaction with alloreactive CTLs and NK cells.