: Fc gamma receptor IIB is an important regulator of immuno-reactivity. Genetic disruption of the Fc gamma receptor results in a fulminate, lupus-like disease in the C57BL/6 murine background. The goal of this project is to more closely examine the lupus which arises in these animals to determine the effect that Fc gamma receptor IIB disruption has on the B cell repertoire and on silencing of auto-reactive B cells in the periphery. In addition, these studies investigate the nature of chromatin tolerance in these animals (i.e. is the loss of tolerance reversible or is it a permanent physiological change) by reestablishment of the Fc gamma receptor IIB regulatory pathway in animals with established autoimmunity.