4may stem from reduced glycosylation of NCSTN. B-1 B cells, T cell-independent antibody response Abstract -secretase is an intramembrane protease complex that catalyzes the proteolytic cleavage of amyloid precursor protein and Notch. Impaired -secretase function is usually associated with the development of Alzheimers disease and familial acne inversa in humans. In a forward genetic screen of mice with allele uncovered in these studies reveals an essential requirement for NCSTN during the type 2 transitional-marginal zone precursor stage and peritoneal B-1 B cell development, the TI antibody response, fur pigmentation, and intestinal homeostasis in mice. B cell responses to antigens are classified as T cell-dependent (TD) or T cell-independent (TI) based on their need for T cell help in antibody production. Antigens eliciting a TD antibody response are proteins that are processed and presented to helper T cells in the context of MHC Rabbit Polyclonal to OR5B3 II molecules. The TD antibody responses are mediated by follicular B cells (also known as B-2 cells, the major B AS-35 cell subset in the body) and are long-lasting to deploy high-affinity antibodies of multiple isotypes. In contrast, TI antigens, such as bacterial capsular polysaccharides and viral capsids, stimulate antibody responses that do not require MHC II-restricted T cell help (1). The TI antibody response is usually mediated by the marginal zone (MZ) and B-1 B cell populations, which expand on immunization in extrafollicular sites (2C4) and confer protective immunity by producing antigen-specific IgM without somatic hypermutation (4C7). Thus, TI responses give rise to less specific but more immediate protection compared with TD antibody responses. B-2 cells are constantly replenished from precursors in bone marrow, where they undergo both positive and negative selection. Immature B cells in bone marrow migrate to the spleen, where they differentiate through two transitional stages and become mature na?ve B-2 cells (8) or, alternatively, MZ B cells. Their fate is determined during the transitional stages and depends on signals from the B cell receptor, B cell activating factor, nuclear factor light chain enhancer of activated B cells, and Notch2, as well as signals involved in anatomical retention of MZ B cells in the spleen (9). In contrast, B-1 cells are generated mainly from fetal liver progenitors rather than bone marrow precursors, reside in the peritoneal cavity, and are maintained by self-renewal throughout the life of the organism (10). It is well established that this spleen is also required for B-1 (especially B-1a) cell development (11); however, the underlying mechanism(s) that mediate B-1 cell differentiation remain largely unknown. The -secretase protease complex cleaves multiple type I membrane proteins, including amyloid precursor protein (APP) and Notch. APP undergoes proteolytic processing by either – or -secretase to release soluble APP ectodomains into the extracellular space. AS-35 Then -secretase cleaves the remaining membrane-anchored APP C-terminal fragments (APP-CTFs) AS-35 and generates AS-35 p3 (the byproduct of – and -secretase cleavages) or amyloid peptides (the byproduct of – and/or -secretase cleavage) together with the APP intracellular domain name (12). Notch plays essential functions in thymic T cell lineage commitment (13), as well as in specification of MZ B cell versus B-2 cell fate (14), and it undergoes a series of proteolytic cleavages by ADAM family metalloproteases and -secretase to generate the Notch intracellular domain name (NICD) (15). The -secretase complex consists of four core subunits: presenilin (PS), PS enhancer 2 (PEN-2), anterior pharynx-defective 1 (APH-1), and nicastrin AS-35 (16). Nicastrin is usually a type I membrane protein with a large extracellular domain name (17) that functions as a -secretase substrate receptor (18). Activation of the -secretase complex requires extensive N-linked glycosylation of nicastrin, which helps stabilize the protein (19). Mutations in -secretase complex proteins and impaired catalytic activity of the complex have been implicated in Alzheimers disease (AD) (20), familial type acne inversa (21), hypopigmentation (22, 23), and thymic hypoplasia (24); however, little is known about the role and function of the -secretase complex in B cell-mediated immunity. Here we describe the effect of a severely hypomorphic but viable missense mutation of on MZ B cell and B-1 B cell development. Results Identification of a Viable Missense Mutation. To identify genes required for the development.