TACI-Ig neutralizes molecules critical for B cell development and autoimmune disease: Impaired B cell maturation in mice lacking BLyS

BLyS and APRIL have similar but distinct biological roles, mediated through two known TNF receptor family members, TACI and BCMA. We show that mice tr eated with TACI-Ig and TACI-Ig transgenic mice have fewer transitional T2 a nd mature B cells and reduced levels of circulating immunoglobulin. TACI-Ig treatment inhibits both the production of collagen-specific Abs and the pr ogression of disease in a mouse model of rheumatoid arthritis. In BLyS-defi cient mice, B cell development is blocked at the transitional T1 stage such that virtually no mature B cells are present, while B-1 cell numbers are r elatively normal. These findings further elucidate the roles of BLyS and AP RIL in modulating B cell development and suggest that BLyS is required for the development of most but not all mature B cell populations found in the periphery.