As the immediate precursors to mature follicular B cells in splenic development, immature transitional cells are an essential component for understanding late B cell differentiation. It has been shown that T2 cells can give rise to mature B cells; however, whether T3 B cells represent a normal stage of B cell development, which has been widely assumed, has not been fully resolved. In this study, we demonstrate both in vitro and in vivo that T3 B cells do not give rise to mature B cells and are instead selected away from the T1-->T2-->mature B cell developmental pathway and are hyporesponsive to stimulation through the BCR. Significantly reduced numbers of T3 B cells in young lupus-prone mice further suggest that the specificity of this subset holds clues to understanding autoimmunity.