Original H-2(d) and alien H-2(k)-like antigens of a BALB/c fibrosarcoma as defined by in vitro and in vivo studies of cell-mediated immunity

The present study examines the immunosensitivity and the immunogenicity of both original H-2(d) and alien H-2(k)-like antigens of the BALB/c (H-2(d)) fibrosarcoma C-1 as detected by in vitro and in vivo cell-mediated cytotoxicity (CMC) assays. It was found that ⁵¹Cr-labeled C-1 cells were lysed in vitro by C57BL/6 anti-H-2(d) lymphocytes. the specificity of this reaction was shown by cold inhibition experiments in which the anti-H-2(d) cytotoxic activity on YC8(H-2(d)) targets was inhibited by unlabeled YC8 or C-1 but not by C3UR11(H-2(k)) tumor cells. Both D(d)- and K(d)-encoded antigens were recognized by appropriate cytotoxic effectors. The immunogenicity of H-2(d) antigens of C-1 was revealed by the ability of C57BL/6 anti-C-1 lymphocytes to lyse YC8 targets. The expression of H-2(k)-like alien alloantigens on C-1 was indicated by the finding that anti-H-2(k) cytotoxic T lymphocytes (CTL), generated by culturing BALB/c spleen cells immune to BALB.K(H-2(k)), C3Hf(H-2(k)) or A(H-2(a)=H-2(k-d)) tissues with the cells of the same strain used for immunization, lysed C-1 targets. The cytotoxicity of these anti-H-2(k)CTL against C3UR11(H-2(k)) targets could be specifically inhibited by cold C3UR11 or C-1 cells but not by two other BALB/c tumors. Using recombinant H-2-congenic mice, it was shown that both D(k) and K(k) antigens were recognized by CTL on C-1 cells. The immunogenicity of the H-2(k)-like antigens, however, could not be detected in vitro. In fact, effector spleen cells from BALB/c immune to C-1 did not develop any detectable cytotoxicity against C3UR11 targets as assayed either by a direct in vitro test or after in vitro restimulation with C-1 sarcoma cells. A similar experimental design was adopted in Winn assays carried out by mixing spleen cells of BALB/c immune mice with either C-1 or C3UR11 targets and injecting the mixtures in BALB/c or hybrid recipients. These in vivo tests revealed the presence of both H-2(d)(K(d) and D(d)) and H-2(k)-like (K(k) and D(k)) antigens on C-1. At variance with the in vitro CMC assays, however, the Winn assay also detected the immunogenicity of the H-2(k) alien antigens, since BALB/c anti-C-1 spleen cells were able to significantly reduce the growth of C3UR11 lymphoma cells in (BALB/c x C3Hf)F₁ hosts.