Studies on the generation and expression of H-2-controlled T helper function in chimeric mice: evidence for two levels of H-2 resitriction.

F1 leads to parental, semisyngeneic/semiallogeneic and fully allogeneic bone marrow radiation chimeras were used as a source of helper T cells in the in vitro anamnestic response to dinitrophenylated keyhole limpet hemocyanin. In F1 leads to parental and in semisyngeneic/semiallogeneic chimeras, a small population of helper T cells restricted to the H-2 haplotype present in the donor only was shown to co-exist with T cells restricted to the shared haplotype. Only the population restricted to the donor H-2 could be demonstrated in allochimeras, presumably due to a lack of antigen-presenting cells of host origin during priming. Under assay conditions where, in addition to T cell/macrophage interactions, a direct T-B cell contact was necessary ("linked" cooperation), the H-2 restrictions observed were absolute. When direct T-B cell contact was made unnecessary by a special experimental protocol ("unlinked" cooperation), H-2 restriction between T and B cells was overcome. Thus, the cellular interactions during the anamnestic immune response to T-dependent antigens seem to be H-2-restricted at two levels: T cell/macrophage and T-B cell interactions.