An induction of a robust IgM memory space by priming with TD antigens has been observed previously (34, 35); our results now determine MZ B cells as the source of this IgM memory space. MZ precursors, but the MZ- and FO-derived GCs were related in VH gene repertoire, somatic mutation, and production of late AFC and IgG Ab. Remarkably, the MZ but not the FO memory space response included IgM Ab. We conclude that MZ B cells are heterogeneous, comprising cells for both Mouse monoclonal to EGFR. Protein kinases are enzymes that transfer a phosphate group from a phosphate donor onto an acceptor amino acid in a substrate protein. By this basic mechanism, protein kinases mediate most of the signal transduction in eukaryotic cells, regulating cellular metabolism, transcription, cell cycle progression, cytoskeletal rearrangement and cell movement, apoptosis, and differentiation. The protein kinase family is one of the largest families of proteins in eukaryotes, classified in 8 major groups based on sequence comparison of their tyrosine ,PTK) or serine/threonine ,STK) kinase catalytic domains. Epidermal Growth factor receptor ,EGFR) is the prototype member of the type 1 receptor tyrosine kinases. EGFR overexpression in tumors indicates poor prognosis and is observed in tumors of the head and neck, brain, bladder, stomach, breast, lung, endometrium, cervix, vulva, ovary, esophagus, stomach and in squamous cell carcinoma. early AFC response and GC/memory space pathway against TD antigens. Keywords: B cells, marginal zone, T-dependent Ag, antibody-forming cells, germinal center Introduction Newly created B cells in adults migrate from BM to peripheral lymphoid cells where they continue to differentiate into functionally and anatomically unique subsets (1). Mature peripheral B cells include B1 cells, which reside primarily Thiomyristoyl in peritoneal and pleural cavities (2), and the conventional B2 B cells. The adult B2 cell populace is definitely heterogeneous, consisting of the major follicular B cells (FO), in LN and splenic lymphoid follicles, and a subset residing in the marginal zone (MZ) of the spleen (3). MZ and FO B cells are distinguished by differential manifestation of several cell surface markers: MZ B cells are IgDlowCD21highCD23low/?, whereas FO B cells are IgDhighCD21interCD23high (4, 5). In addition, MZ B cells communicate numerous activation markers, such as high basal levels of CD80, CD86, CD40, and CD44, and low level of CD62L (5, 6). As a functional corollary, MZ B cells show quick and strong proliferation and Ig secretory reactions to activation with LPS, anti-IgM, and CD40 ligands (5C7). The apparent hyperreactivity of MZ B cells and their unique anatomic localization in the reddish pulp junction strongly suggest that these B cells mediate quick Ab reactions to blood-born antigens (8). There is increasing evidence for selection of B cells into the MZ or follicular pool through B cell receptor (BCR)Cmediated signals (9, 10). Studies on transgenic mice shown that Thiomyristoyl B cells expressing BCR with specificity for different Ags experienced accumulated either in the follicles or in the MZ (11). In particular, B cells specific for the bacterial epitope, phosphorylcholine, homed to MZ and responded to the TI form of Thiomyristoyl the Ag (3, 11). The ligands that control cellular selection and homing are Thiomyristoyl not known (3). Interestingly, in humans (12, 13), and to a lesser degree in rats (14), some MZ B cells communicate somatically mutated IgV genes, suggesting that they already experienced Ags and became memory space cells. Collectively, these findings suggest that the repertoire of MZ B cells is definitely skewed by activation with environmental Ags. Fagarasan and Honjo (15) proposed that MZ B cells respond to T-independent Ags (TI) and may not be controlled by T cells. This notion was based primarily within the phenotype of Pyk-2Cdeficient mice (16) that experienced a severely reduced MZ B cell populace and diminished Ab response to TI type I Ag (TI-I) and TI type II Ag (TI-II). However, this defect was restricted only to the IgG2a and IgG3 isotypes, whereas IgG1 and IgG2b Ab reactions to TI-I and TI-II Ags were unaffected. Moreover, the disruption of Pyk-2 also inhibited the IgM response to T-dependent Ags (TD). These conflicting observations suggest that the function of MZ B cells and their relationship with T cells are complex. Indeed, Tanigaki et al. (17) failed to find a relationship between MZ B cells and TI Ab reactions. They generated mice lacking manifestation of RBP-J, a mediator of Thiomyristoyl Notch signaling, in B cells using conditional mutagenesis. Such mice experienced no MZ B cells, but Ab reactions to TI-I, TI-II, and TD Ag were unaffected. The phenotypes of the Pyk-2 (16) and RBP-J (17) mutants have shown that MZ B cells are not dedicated only to TI Ab reactions. MZ B cells present Ags and deliver costimulatory signals to T cells more efficiently than FO B cells in vitro (5), suggesting that MZ cells can mount quick Ab responses requiring cognate T cell help (18). Indeed, using a hapten-carrier system, Liu et al. (19) shown a rapid appearance of specific, hapten-binding MZ B cells in rats that had been primed previously to the carrier protein. We hypothesized the Ab response of MZ B cells to TD Ags is definitely qualitatively different from that of FO B cells and that the two cell subsets differ in their potential to form antibody-forming cells (AFC), germinal centers (GCs), and memory space cells. To test this prediction rigorously, we reconstituted mice with purified MZ and FO B cells from naive WT C57BL/6 donors,.