T cells from fully H-2 allogeneic (A replaced by B) radiation bone marrow chimeras are functionally competent and host restricted but are alloreactive against hybrid Ia determinants expressed on (A x B)F1 cells.

In this communication it is demonstrated that T cells from fully allogeneic A replaced by B radiation bone marrow chimeras are alloreactive against the hybrid Ia molecules expressed on the surface of heterozygous A X B cells. These results suggested that previous failures to generate cytotoxic T lymphocyte (CTL) responses from fully allogeneic chimeras by sensitizing the chimeric T cells to antigen in an (A X B)F1-priming environment might have been confounded by an ongoing alloreaction against determinants created by hybrid Ia molecules expressed on F1 cells. Consequently, the ability to generate CTL responses from fully allogeneic chimeras was re-examined by sensitizing the chimeric T cells to antigen presented by homozygous rather that F1 stimulator cells. It was found that T cells of donor bone marrow origin that mediate cytotoxic responses to trinitrophenyl-modified self determinants do differentiate into functional competence in an H-2-incompatible host environment and are restricted to the host H-2 haplotype.