Monogamous T helper cell

Abstract

HUMORAL antibodies are produced by lymphocytes of bone-marrow or bursal origin (B cells). Some antigens are apparently capable of stimulating B cells and inducing a response directly but many other antigens are dependent on the cooperative help of lymphocytes of thymic origin (T cells). There are at least two forms of such cooperation between B and T cells. One type of cooperation is ‘nonspecific’ where T cells once activated by specific antigen release a nonspecific factor which can then facilitate the responses of B cells to certain other non-related antigens¹. The other well studied cooperative mechanism is known as ‘specific cooperation’ and classically this has been analysed with the use of ‘hapten-carrier’ systems². The exact nature of this cooperative event is not known. It may be that cooperation occurs through widely diffusible specific factors released by T cells, or alternatively the cooperating T and B cells may need to come into close or direct contact. We have studied helper T-cell function in a microculture system with the aim of determining whether a single helper T cell could activate one or many B cells. Experiments of this type have previously been performed by repopulating mice with limiting numbers of immunocompetent cells and examining the resulting foci of antibody activity. When T cells were the limiting population some have found these foci to be heterogeneous³ and others have found them to be monoclonal^4,5. Similar in vitro studies have also suggested marked restriction in the B-cell response where T helper cells were limiting⁶. Here we present direct evidence to support the findings demonstrating restriction. We conclude that in the conditions used, one specific helper T cell cooperated with one B cell only.