Relative roles of somatic and Darwinian evolution in shaping the antibody response.

The need for a highly specific system of recognition in immunity has resulted in the evolution of several somatic mechanisms such as V(D)J recombination, to diversify the repertoire of B cells. Therefore, repertoire diversification is the driving force for the cells that constitute the bulk of the response to unpredictable pathogens, the B2 naive B cells. Predictability of antigen, on the other hand, has played a major role in shaping the neonatal repertoire, in which evolution to recognize commonly encountered pathogens has driven the germline sequence of several VH segments that are used frequently in the neonatal repertoire. A third population, the memory B cell population, is generated to respond to a known pathogen, but predictability of the pathogen is not acquired until after a first exposure. Therefore, it is somatic evolution in germinal centers that drives the generation of high-affinity memory B cells.