Evidence for non-identity of T killer and T helper cells sensitised to allogeneic cell antigens

Abstract

BONE marrow-derived lymphocytes (B cells) can be triggered for antibody synthesis by a stimulus from immunocompentent allogeneic¹ or xenogeneic² lymphoid cells. The stimulus was shown to act directly on the B cell, since a response may occur in the absence of syngeneic thymus-derived lymphocytes (T cells)¹ and is possible even to a hapten². This observation has led to the hypothesis that cooperating T cells (T-helper) are identical to cytotoxic T cells (T-killer) and act on B cells by surveying them for immunogen bound to their cell surface³. The T cells recognise the cell-bound immunogen and emit a sublethal signal to the B cells, triggering them to produce antibody. But the question arises, whether this is the way triggering of B cells usually occurs in the immune response. Recent experiments have shown that T cells sensitised to foreign erythrocyte antigens are able to cooperate with B cells to induce humoral antibody synthesis, but are not able to perform cytotoxic lysis of erythrocyte target cells^4,5. T helper cells therefore need not be cytotoxic to the sensitising antigen to trigger B cells. This finding led to more extensive experiments concerning the question of whether T killer and T helper functions are performed by the same cell or not.