< 0
< 0.01 comparing the response from B-2 cells with and without EGTA. Majority of the Ca2+ flux seen in B-2 cells upon BCR + CD19 stimulation is through PI3K activity. active pLyn which appears to have an inhibitory role. The CD19 induced Ca2+ response and BCR induced proliferation response were restored by a partial inhibition of pLyn with Src kinase specific inhibitors. These findings suggest a defect in CD19 mediated signals in both peritoneal and splenic B-1 B lymphocytes, which is in part, due to higher levels of constitutively active Lyn. Keywords: mouse B-1 cells, B cell receptor, CD19 signaling INTRODUCTION B-1 cells are distinguished from B-2 cells based on their anatomical localization, cell surface phenotype, self-renewal capacity, B cell PTC-209 HBr receptor signal generation, and contribution to natural circulating serum IgM (Berland and Wortis, 2002; Hayakawa et al., 1985; Hayakawa et al., 1984; Hayakawa et al., 1986). PTC-209 HBr B-1 cells are localized in the coelomic cavities (peritoneal and pleural), Peyers patches, tonsils, and spleen (~5% of splenic B cells) and absent in lymph nodes. B cell activation initiates a cascade of intracellular signaling events leading to cell proliferation, differentiation and secretion of the antibody or apoptosis. Binding of antigen or its surrogate, anti-IgM leads to clonal expansion in the follicular (FO) or the conventional B-2 B cells. Unlike B-2 cells, B-1 cells are hyporesponsive to BCR cross-linking and share some similarities with anergic cells (Hippen et al., 2000). Paradoxically, B-1 cell numbers are increased in several murine models of autoimmune disorders, such as NZB, MRL/lpr and motheaten mice, as well as in humans with lupus or rheumatoid arthritis (Burastero et al., 1988; Dauphinee et al., 1988; Hayakawa et al., 1983; Mohan et al., 1998; Sidman et al., Rabbit Polyclonal to NPM (phospho-Thr199) PTC-209 HBr 1986). In blood, rheumatoid factor producing B cells were found to be predominantly B-1 type (Haas et al., 2005; Hardy et al., 1987). B-1 cells are further subdivided into B-1a and B-1b subtypes as the former but not the latter express CD5 (Stall et al., 1992). Bikah showed that CD5 down regulates BCR signaling by recruiting SHP-1 (Src homology 2 (SH2) domain containing protein tyrosine phosphatase-1) into the BCR complex (Sen et al., 1999). PTC-209 HBr More recently, Dal Porto showed that CD5 may induce activation of Lck which may in turn inhibit BCR signaling in B-1 cells (Dal Porto et al., 2004). This, however, is controversial since Frances showed that B-1 cells do no express Lck (Frances et al., 2005). We have shown that FACS sorted peritoneal B-1a and B-1b B cells are equally defective in BCR induced proliferative response (Sen et al., 2002). B-1a and B-1b B cells collaborated in immunity to by respectively contributing to innate and adaptive immune responses (Haas et al., 2005). Since B-1b cells do not express CD5, the basis of BCR signaling defect is unclear. Recently, it has been shown that B-1b B cells may be primarily responsible for IgM memory cells, as they were expanded preferentially in a murine model of relapsing fever (Alugupalli et al., 2004). B-1b B cells have thus gained attention as crucial players of cell mediated antibody responses independent of T cell help (Alugupalli, 2008). Recent description of IL-10 producing splenic CD1dhi CD5+ B cells in mice with a regulatory role reinforces the importance of B-1 B cells in T-cell mediated immunity (Yanaba et al., 2008). These regulatory B cells (Breg) are proposed to suppress activation and differentiation of CD4+, CD8+, NKT and other immune cell types thereby demanding caution in B cell depletion therapeutics as it may hinder maintenance of tolerance (Mauri and Ehrenstein, 2008). The B cell restricted glycoprotein CD19 in concert with CD21/CR2 and CD81/TAPA-1 forms a co-receptor PTC-209 HBr complex and aids in BCR function as a positive regulator of B cell signaling by lowering the threshold for B cell activation (Carter and Fearon, 1992). Activation of CD19 is dependent upon Lyn-mediated phosphorylation of CD19 cytoplasmic domain (Fujimoto et al., 2001). There are 9 conserved tyrosine residues on.