ABSTRACT
It is commonly admitted that an antigen, or a processed antigen, is first presented to a T cell by a macrophage or some other antigen-presenting cell, bearing an MHC molecule compatible with the T-cell receptor. The T cell thus activated, when encountering a B cell, tests for the presence of the same antigen, through a similar mechanism of MHC-dependent antigen presentation. When a B cell engages into a program of extensive somatic diversification of its immunoglobulin genes, there is a potential risk of increased mutation rate in other genes3 and, in particular, the MHC genes. A minority of B cells would be capable of antigen presentation. The majority of B cells, issued from extensive somatic diversification would have extremely limited capacities for antigen presentation. Each antigen may, in principle, be uniquely characterized by its set of binding energies to a large collection of antibodies.
