TACI-dependent APRIL signaling maintains autoreactive B cells in a mouse model of systemic lupus erythematosus.

Autoantibodies contribute to the development of systemic lupus erythematosus (SLE). APRIL (a proliferation-inducing ligand), a member of the TNF superfamily, regulates plasma-cell survival and binds to TACI (transmembrane activator CAML interactor) and BCMA (B-cell maturation antigen). We previously showed that APRIL blockade delayed disease onset in lupus-prone mice. In order to evaluate the role of APRIL receptors in the development of SLE, APRIL, TACI, BCMA, or double TACI.BCMA null mutations were introduced into the Nba2.Yaa (Y-linked autoimmune acceleration) spontaneous lupus mouse model. Mortality as a consequence of glomerulonephritis (GN) was reduced in Nba2.APRIL-/- .Yaa, Nba2.TACI-/- .Yaa and double-KO mice compared with Nba2.Yaa mice and correlated with lower levels of circulating antibodies, while splenic populations remained unchanged. In contrast, the appearance of symptoms was accelerated in BCMA-deficient mice, in which TACI signaling was increased. Finally, lupus-prone mice deficient for the APRIL-TACI axis produced less pathogenic antibodies and developed less GN. Disease reduction was attributed to impaired T-independent type 2 responses when the APRIL-TACI signaling axis was disrupted. Collectively, our results have identified and confirmed APRIL as a new target involved in B-cell activation, in the maintenance of plasma cell survival and subsequent increased autoantibody production that sustains lupus development in mice.