Carrier specificity and the allogeneic effect in mice

Abstract The findings of several investigators suggest that in vitro soluble T cell factors, non‐antigen specific, can replace helper T cells in the induction of antibodies. The present experiments set limits to the possible range of action of such factors in the in vivo induction process. Murine cells primed with a hapten‐carrier complex could not be efficiently stimulated to produce anti‐hapten antibody by injection of the carrier alone or together with the hapten on an unrelated carrier. This reconfirms the requirement of physical union between hapten and carrier for efficient secondary stimulation. Even under conditions of presumably maximal production of non‐antigen specific T cell product, namely in a graft‐versus‐host reaction, there was no evidence for the systemic appearance of such a factor. A graft‐versus‐host reaction could substitute for specific helper cells only when the hapten‐primed cells were the targets in the cellular reaction and did not belong to the aggressor cell population. The allogeneic effect was shown to be T cell‐dependent and to correlate with reactivity in mixed lymphocyte reaction. In most instances, efficient allogeneic stimulation of the secondary anti‐hapten response required the presence of both allogeneic aggressor cells and hapten on a heterologous carrier. Very low numbers of allogeneic cells (around 10 4 T cells per host) sufficed to abrogate carrier specificity almost completely. This suggests that some type of amplification mechanism is involved in mediating the allogeneic effect. The results support the concept that in vivo , efficient antibody induction relies on cell‐cell interaction mediated by antigen bridging or by allogeneic recognition.