HLA-DQw6 transgenic C57BL/6 mice (DQw6-B6) were utilized to define the role of HLA-DQw6 gene product in immune-recognition. To investigate the responsiveness of lymph node cells from C57BL/6 mice (B6) or DQw6-B6 in response to DQw6 molecules expressed in the DQw6-B6, in vitro secondary MLR was performed. The lymph node cells from B6 proliferated in response to spleen cells from DQw6-B6, whereas those from DQw6-B6 did not. These results suggested that DQw6-B6 acquired tolerance to DQw6 molecules. The difference of T cell repertoire between B6 and DQw6-B6 was investigated using mAbs directed against T cell receptor V beta regions, V beta 3, V beta 5, V beta 6, V beta 8, V beta 11 and V alpha 3.2. Although the proportion of V beta 5+ CD8+ T cells and V beta 6+ CD4+ T cells were increased in the B6 anti-DQw6-B6 MLR T cell line, there was no significant difference in the proportion of peripheral T cells expressing each V alpha or V beta region between B6 and DQw6-B6. Both CD4+ and CD8+ long term-cultured T lymphocyte cell lines were generated from lymph node cells of B6 stimulated in vitro by irradiated spleen cells from DQw6-B6. The CD4+ T cell line proliferated in response to spleen cells of DQw6-B6 or L cell transfectant expressing HLA-DQw6 molecules and these responses were completely inhibited by either anti-DQ or anti-CD4 monoclonal antibodies (mAbs) but not by anti I-Ab mAbs. The CD8+ T cell line lysed splenic cells activated by lipopolysaccharide (LPS) from DQw6-B6 spleen cells but not from B6. The CD8+ T cell line also exhibited a cytotoxicity to splenic LPS blast cells from backcross progenies between (DQw6-B6 x DBA1) F1 and DBA1, only when target cells expressed both HLA-DQw6 molecules and H-2b. These observations indicated that recognition of HLA-DQw6 by the CD8+ cytotoxic T cell line was restricted by H-2b. The cytolytic activity of the CD8+ T cell line was inhibited by either anti-CD8 or anti-H-2Db mAbs but not by anti-HLA-DQ nor anti-H-2Kb mAbs. These results show that HLA-DQ transgene products expressed in DQw6-B6 can induce xenogeneic MLR in both CD4+ and CD8+ T cells. The CD4+ T lymphocytes recognize the HLA-DQw6 molecule itself whereas the CD8+ cytotoxic T lymphocytes recognize the HLA-DQw6 gene product in the context of H-2Db.