Expression of H-2^b alloantigens in a variant of a moloney virus-induced YAC (H-2^a) lymphoma

Splenocytes of A(H-2^a), BALB/c(H-2^d) and C57BL/6(H-2^b) mice that were sensitized against several allogeneic normal lymphocytes and lymphoma cells in mixed lymphocyte cultures (MLC) and mixed lymphocyte-tumor cell cultures (MLTC) exhibited the expected cell-mediated cytotoxic responses against normal and tumor cells carrying the relevant alloantigens. In contrast, strong cytotoxic reactivity cross-reactive with C57 BL/6 target cells was observed when a variant of YAC lymphoma (YAC-b) of strain A mice were employed either as sensitizers or as targets. Furthermore, this 'unpredicted' cross-reactivity was also obtained with syngeneic responder splenocytes sensitized to YAC-b cells. The possibility that the nonspecific cytotoxicity was caused by activation of natural killer (NK) cells in the culture was excluded by the finding that the cytotoxic capability of sensitized effector cells was greatly diminished by treatment with anti-Thy 1.2 serum and complement. Serologic analysis with anti-H-2 alloantisera revealed that the YAC-b tumor line, but not the parental YAC lymphoma, carried H-2^b alloantigens. It is concluded that the 'unpredicted' cytotoxic responses here observed is a result of conventional antigen recognition and of specific sensitization to alien H-2^b components expressed on the YAC-b subline.