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

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Abstract
The present study examines the immunosensitivity and the immunogenicity of both original H‐2d and alien H‐2k‐like antigens of the BALB/c (H‐2d) 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 C 57 BL/6 anti‐H‐2d lymphocytes. The specificity of this reaction was shown by cold inhibition experiments in which the anti‐H‐2d cytotoxic activity on YC8 (H‐2d) targets was inhibited by unlabeled YC8 or C‐1 but not by C3UR11 (H‐2k) tumor cells. Both Dd‐ and Kd‐encoded antigens were recognized by appropriate cytotoxic effectors. The immunogenicity of H‐2d antigens of C‐1 was revealed by the ability of C 57 BL/6 anti‐C‐1 lymphocytes to lyse YC8 targets. The expression of H‐2k‐like alien alloantigens on C‐1 was indicated by the finding that anti‐H‐2k cytotoxic T lymphocytes (CTL), generated by culturing BALB/c spleen cells immune to BALB.K (H‐2k), C3Hf (H‐2k) or A (H‐2a = H‐2k/d) tissues with the cells of the same strain used for immunization, lysed C‐1 targets. The cytotoxicity of these anti‐H‐2k CTL against C 3 UR11 (H‐2k) targets could be specifically inhibited by cold C 3 UR 11 or C‐1 cells but not by two other BALB/c tumors. Using recombinant H‐2‐congenic mice, it was shown that both Dk and Kk antigens were recognized by CTL on C‐1 cells. The immunogenicity of the H‐2k‐like antigens, however, could not be detected in vitro. In fact, effector spleen cells from BALB/c mice immune to C‐1 did not develop any detectable cytotoxicity against C 3 UR 11 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 C3 UR 11 targets and injecting the mixtures in BALB/c or hybrid recipients. These in vivo tests revealed the presence of both H‐2d (Kd and Dd) and H‐2k‐like (Kk and Dk) antigens on C‐1. At variance with the in vitro CMC assays, however, the Winn assay also detected the immunogenicity of the H‐2k alien antigens, since BALB/c anti‐C‐1 spleen cells were able to significantly reduce the growth of C 3 UR 11 lymphoma cells in (BALB/c × C 3 Hf)F1 hosts.