Influence of the major histocompatibility complex on lymphocyte interactions in antibody formation

PRODUCTS of the major histocompatibility gene complex (MHC) play an important part in regulating immune responses, particularly responses involving the participation of thymus-derived (T) lymphocytes. It seems that wherever the situation has been carefully examined, T cells exhibit a dual specificity; that is, specificity for, on the one hand, structures expressed by the MHC and, on the other, for foreign antigenic determinants. Thus, in the mouse, cytotoxic T cells show specificity for H–2K or H–2D (refs 1, 2) determinants, whereas those involved in delayed type hypersensitivity3 and those which help in antibody formation4 show specificity for the I region. The nature of MHC restrictions exhibited by cytotoxic cells has been much clarified by the studies of Bevan5 which suggest, and of those of Zinkernagel et al.6, which show, that precursors of cytotoxic T cells are probably selected for their capacity to recognise particular H–2 markers during their differentiation in the thymus, and that this ‘learning’ process is not influenced by the H–2 haplotype of the T cells themselves. The data presented here suggest that a comparable situation exists for T lymphocytes (helper T cells) participating in antibody production.