Transmembrane activator and calcium-modulating cyclophilin ligand interactor (TACI), also known as tumor necrosis factor receptor superfamily member 13B (TNFRSF13B) and cluster of differentiation 267 (CD267), is a single-pass type III membrane receptor that is highly expressed on the surface of mature innate-like B cells, such as marginal zone and B-1 B cells in mice, and memory B cells in humans. TACI/TNFRSF13B/CD267 is also expressed on the surface of activated T cells, while monocytes and dendritic cells express lower levels of TACI/TNFRSF13B/CD267 primarily intracellularly. TACI/TNFRSF13B/CD267 is the receptor for soluble ligands BAFF/TNFSF13B and APRIL/TNFSF13. Upon ligation, TACI/TNFRSF13B/CD267 recruits tumor necrosis factor receptor-associated factor (TRAF) family members and calcium signal-modulating cyclophilin ligand (CAMLG) in order to activate NFAT, NF-kappaB, and AP-1 transcriptional programs. TACI/TNFRSF13B/CD267 is necessary for T cell-independent type II and type I responses, negative regulation of B cell and T follicular helper cell numbers, and promotion of class switch recombination in B cells. Mutations and aberrant regulation of TACI/TNFRSF13B/CD267 has been associated with cancer, autoimmune diseases, and immunodeficiency disorders. Multiple isoforms produced by alternative splicing have been identified.
