Cooperation across the histocompatibility barrier

Abstract

STUDIES in mechanisms of T–B collaboration in the immune response have shown that T cells can produce factors after stimulation with antigen^1–3, allogeneic cells^4–6, or mitogens (ref. 7 and O. Sjöberg, unpublished), that can stimulate B cell responses to antigens. Such factors have been categorised as specific^1,3 or nonspecific (refs 4–7 and O. Sjöberg, unpublished). Studies have shown that the specific factor produced by (T,G–A—L) stimulation of educated T cells⁸ is able to promote antibody formation by both syngeneic and allogeneic cells. Similarly, with one exception⁶, nonspecific factors from antigen- or mitogen-activated T cells were able to cooperate with B cells from histoincompatible strains^7,9. Reports that histoincompatible T and B cells could not be demonstrated to cooperate in a humoral immune response¹⁰, in conditions in which it was consided that inhibitory allogeneic effects were excluded or irrelevant, indicated that for efficient collaboration T and B cells need to share surface determinants coded for by major histocompatibility complex (MHC), in particular the I region or its equivalent. One report¹¹ argued against this;allophenic mice (C3H + C57BL) were able to make non-responder allotype towards (T,G)–A—L. This finding made the presumption that it was the high responder T cells which were collaborating with the low responder B cells, but could not exclude that alternative cooperative mechanisms were operational.