TACI, (Transmembrane activator and CAML interactor)

The protein encoded by this gene is a lymphocyte-specific member of the tumor necrosis factor (TNF) receptor superfamily. It interacts with calcium-modulator and cyclophilin ligand (CAML). The protein induces activation of the transcription factors NFAT, AP1, and NF-kappa-B and plays a crucial role in humoral immunity by interacting with a TNF ligand. This gene is located within the Smith-Magenis syndrome region on chromosome 17. [provided by RefSeq, Jul 2008]

TNFRSF13B: Receptor for TNFSF13/APRIL and TNFSF13B/TALL1/BAFF/BLYS that binds both ligands with similar high affinity. Mediates calcineurin-dependent activation of NF-AT, as well as activation of NF-kappa-B and AP-1. Involved in the stimulation of B- and T- cell function and the regulation of humoral immunity. Defects in TNFRSF13B are the cause of immunodeficiency common variable type 2 (CVID2). CVID2 is a primary immunodeficiency characterized by antibody deficiency, hypogammaglobulinemia, recurrent bacterial infections and an inability to mount an antibody response to antigen. The defect results from a failure of B-cell differentiation and impaired secretion of immunoglobulins; the numbers of circulating B-cells is usually in the normal range, but can be low. Defects in TNFRSF13B are a cause of immunoglobulin A deficiency 2 (IGAD2). Selective deficiency of immunoglobulin A (IGAD) is the most common form of primary immunodeficiency, with an incidence of approximately 1 in 600 individuals in the western world. Individuals with symptomatic IGAD often have deficiency of IgG subclasses or decreased antibody response to carbohydrate antigens such as pneumococcal polysaccharide vaccine. Individuals with IGAD also suffer from recurrent sinopulmonary and gastrointestinal infections and have an increased incidence of autoimmune disorders and of lymphoid and non-lymphoid malignancies. In vitro studies have suggested that some individuals with IGAD have impaired isotype class switching to IgA and others may have a post-switch defect. IGAD and CVID have been known to coexist in families. Some individuals initially present with IGAD1 and then develop CVID. These observations suggest that some cases of IGAD and CVID may have a common etiology. 2 isoforms of the human protein are produced by alternative splicing.

Protein type: Membrane protein, integral; Receptor, misc.; Cell cycle regulation

Chromosomal Location of Human Ortholog: 17p11.2

Cellular Component: integral to plasma membrane; external side of plasma membrane

Molecular Function: protein binding; receptor activity

Biological Process: cell surface receptor linked signal transduction; B cell homeostasis; hemopoietic progenitor cell differentiation; negative regulation of B cell proliferation

Disease: Immunodeficiency, Common Variable, 2; Immunoglobulin A Deficiency 2