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We report that the tumor neurosis factor homolog APRIL (a proliferation-inducing ligand) stimulates in vitro proliferation of primary B and T cells and increases spleen weight due to accumulation of B cells in vivo. APRIL functions via binding to BCMA (B cell maturation antigen) and TACI (transmembrane activator and CAML-interactor) and competes with TALL-1 (also called BLyS or BAFF) for receptor binding. Soluble BCMA and TACI specifically prevent binding of APRIL and block APRIL-stimulated proliferation of primary B cells. BCMA-Fc also inhibits production of antibodies against keyhole limpet hemocyanin and Pneumovax in mice, indicating that APRIL and/or TALL-1 signaling via BCMA and/or TACI are required for generation of humoral immunity. Thus, APRIL?TALL-1 and BCMA-TACI form a two ligands?two receptors pathway involved in stimulation of B and T cell function. [ABSTRACT FROM AUTHOR]

Presents information on a study which described B cell hyperplasia and autoimmune lupus-like changes in transgenic mice expressing TALL-1 under the control of a beta-actin promoter. Effectiveness of TALL-1 as a mediator in B cell-associated autoimmune diseases; Antibodies associated with lupus in TALL-1 transgenic mice; Results of the study.