The one signal theory of B cell activation revisited: A role for surface immunoglobulin in regulating T‐independent antibody responses?

Summary Early theories of antibody production by B cells achieved considerable success in predicting B cell behaviour with simple deductive models. One such model, the one signal theory, postulated that the antigen receptor on B cells played only a passive non‐signalling role in focusing non‐specific activating signals to the B cell surface. This prediction is at least partially consistent with recent discoveries concerning the helper signals delivered to B cells by T cells. Here, we re‐examine the foundation of this theoretical prediction with the benefit of recent information. The experimental basis for the theory was a study of B cell activation by LPS and, in particular, the interpretation of a bell‐shaped dose‐response curve. The logic applied is appropriate to explain some, but not all, forms of B cell behaviour because, as is now clear, the role played by the antigen signal varies depending upon the method of activation. This re‐examination suggests an alternative interpretation of the LPS‐induced bell‐shaped curves that incorporates a role for an antigen signal. If correct, the mechanism would ensure that T‐independent responses are drawn from low affinity precursors.