DOES POSITIVE SELECTION DETERMINE THE B-CELL REPERTOIRE

To know whether each newly formed B cell has an equal chance of surviv al in the organism, we analyzed the composition of the B cell repertoi re of extremely limited diversity by generating mu-transgenic kappa-kn ockout mice. Surprisingly, in both types of mice studied, the B cell r epertoire is mainly composed of cells expressing the mu-transgene-enco ded chain associated with only one out four available lambda types dep ending on the mu transgene. Moreover, B cell differentiation cultures in vitro show that newly formed B cells can express the various lambda types regardless of the presence or absence of the mu transgenes. The se results show a drastic impact of the heavy chain on the lambda ligh t chain repertoire expressed in the periphery. The overexpression of a unique heavy/light chain pairing therefore results from selective pro cesses. The immature B cells may be positively selected to provide the immunocompetent B cells in the periphery.