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

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.