EXPRESSION OF MEDIAL CLASS-I HISTOCOMPATIBILITY ANTIGENS ON RMA-S MUTANT-CELLS

The RMA-S mutant T cell line is defective in H-2b restricted antigen presentation and has markedly reduced surface expression of K(b) and D(b). We examined RMA-S for the expression of the medial class I histocompatibility antigens Qa1b and Mta. While RMA-S targets varied in their susceptibility to lysis by cytotoxic T lymphocytes (CTL) specific for Qa1b, Mta levels were detectable but consistently low compared to the parent RMA cell line. Addition of synthetic ND1-alpha-1 - 26 or ND1-alpha-1 - 17 peptides that mimic MTF-alpha (the ligand of Mta) increased killing of RMA-S by anti-Mta-alpha CTL to levels comparable to or better than RMA, with 300 nM peptide being fully effective. None of the MTF peptides increased the killing of RMA-S by anti-H-2b or anti-Qa1b CTL, even at the highest (1-mu-M) peptide concentrations. RMA-S cells treated with 100-mu-M of either the ND1-alpha-4 - 26 or ND1-alpha-1 - 26 peptides showed a small increase in the fluorescent staining for beta-2-microglobulin but not for H-2K(b) or H-2D(b). These results show that Mta and Qa1b, although affected, are not obliterated by the defect in RMA-S cells; that the association of MTF peptides with HMT is exclusive; and that MTF enters the endoplasmic reticulum in the same fashion as other endogenous peptides.