IMPAIRMENT OF T-CELL-DEPENDENT B-CELL RESPONSES AND B-1 CELL-DEVELOPMENT IN CD19-DEFICIENT MICE

CD19 is the hallmark differentiation antigen of the B lineage. Its ear ly expression has implicated a role for CD19 during the antigen-indepe ndent phases of B-cell development, whereas in mature B cells CD19 can act synergistically with surface immunoglobulin to induce activation( 1). We have generated CD19-deficient mice and found that development o f conventional B cells is unperturbed. However, mature CD19(-/-) B cel ls show a profound deficiency in responding to protein antigens that r equire T-cell help. This is accompanied by a lack of germinal centre f ormation and affinity maturation of serum antibodies. Thus CD19 is cru cial for both initial B-cell activation by T-cell-dependent antigens a nd the maturation and/or selection of the activated cells into the mem ory compartment. An impairment in ligand-driven selection may also be responsible for the observation of a striking reduction in the B-1 (fo rmerly Ly-1) B-cell subset, thought to develop under the control of se lf-antigens and bacterial antigens (reviewed in ref. 2).