Role of antigen in later stages of B cell development (153.20)

Abstract

Abstract B cell development occurs in the gut associated lymphoid tissue (GALT) of many mammals and birds. In chickens, the early stages of B cell development, including colonization of bursal follicles, B cell proliferation within bursal follicles and repertoire diversification by gene conversion, are supported by surface Ig receptor related constructs that lack antigen binding capacity. Thus early B cell development requires Ig receptor expression but not sIg ligation. In contrast later stages of bursal development, including cortico-medullary redistribution of B cells and their maintenance after hatch, is not supported by those constructs. The later stages of bursal B cell development occur in the presence of gut derived antigens suggesting the possibility that later stage may require antigen mediated sIg receptor ligation as opposed to simply receptor expression. To address this directly, we have introduced Ig receptor related constructs with defined antigen specificity into developing chick embryos. Expression of such constructs is sufficient to support early stages of B cell development, and in the absence of cognate antigen, is not sufficient to support the later stages of B cell development. Preliminary evidence suggests, however, that introduction of cognate antigen results in extended maintenance of receptor expressing B cells after hatch suggesting that ligation of the BCR may act as a survival signal in the later stages of B cell development in the bursa.