XBP-1, a transcription factor that drives the unfolded protein response (UPR), is activated in B cells when they differentiate to plasma cells. mice. We find that XBP-1-deficient mice have a robust plasma cell population in the spleen and high titers of serum antibodies after one immunization. This robust antibody response is short lived due to a defect in the plasma cell colonization of long-lived niches in the bone marrow. Results XBP-1KO/MD4 B cells do not sustain antibody secretion To investigate the role of XBP-1 in B-cell responses to antigen, we generated CD19-Cre XBP-1flox/flox/MD4 transgenic (XBP-1KO/MD4) mice, in which >95% of B cells express a BCR specific for the HEL. We examined the B-cell compartment (bone Obatoclax mesylate marrow, peritoneal cavity and spleen) of XBP-1KO/MD4 mice and found normal numbers of B cells, including pro-B, pre-B and immature B cells in bone marrow, as well as normal B1 and B2 compartments in the peritoneal cavity and spleen. Transitional B-cell populations, marginal zone B cells and germinal centre B cells were also unaffected by XBP-1 deficiency. The number of CD138+ long-lived plasma cells in the bone marrow and spleen was extremely low in these mice, as they expressed the MD4 transgene and had never been exposed to the relevant antigen, HEL (Figure 1A and B). We repeatedly immunized mice with HEL and found that the anti-HEL IgM in the sera of XBP-1KO mice was significantly lower than that of XBP-1WT mice (Figure 1C; see also Figure 7C), a phenotype consistent with the block in plasma cell differentiation seen in XBP-1?/?/RAG2?/? chimeric mice (Reimold and Igand Syk on antigen-specific activation of the BCR B cells were harvested from the spleens of XBP-1WT/MD4 and XBP-1KO/MD4 mice, cultured with LPS for 3 or 4 4 days and activated with trimeric HEL as a physiological means of engaging the BCR through its antigen-binding sites, rather than by cross-linking through conserved Obatoclax mesylate portions of the BCR (Kim transcripts. The translation product, XBP-1s, Rabbit polyclonal to EIF4E. then upregulates transcription of ER chaperones, relieving ER stress and allowing the nascent plasma cell to continue producing IgM. In the absence of XBP-1, misfolded IgM presumably accumulates in the ER and leads to apoptosis, thus explaining the lack of plasma cells in XBP-1-deficient mice (Iwakoshi and data not really demonstrated). IL-6, itself a glycoprotein, can be secreted normally from XBP-1-lacking plasmablasts on ligation of TLRs (Shape 5B and C). Signalling through the IL-4 receptor and through TLRs 4 and 9 can be uncompromised in XBP-1-deficient B cells, offering further evidence these receptors are practical and correctly folded (Shape 5ACC). To raised understand the part of XBP-1 in plasma cell differentiation as well as the problems in XBP-1-lacking cells, we analysed the B cell-specific Obatoclax mesylate XBP-1 knockout/MD4 transgenic (XBP-1KO/MD4) mouse, where B cells communicate an HEL-specific BCR encoded with a transgene (Goodnow by immediate binding to a conserved Obatoclax mesylate noncoding series between exons 5 and 6 (Sciammas and so are neither immediate nor indirect focuses on of XBP-1 (Acosta-Alvear transcription (Shaffer mRNA. Of take note, XBP-1 deficiency significantly enhances IRE-1 proteins levels (Shape 2C; Supplementary Shape S1), demonstrating responses inhibition of XBP-1 manifestation Obatoclax mesylate on IRE-1, identical to what sometimes appears in hepatocytes (Lee et al, 2008). We suggest that XBP-1 activation in B cells can be a differentiation-dependent event, which the failing of XBP-1-lacking B cells to be plasma cells requires misregulation of crucial transcription factors, because of altered BCR signalling possibly. Paradoxically, lack of XBP-1 qualified prospects to improved IRF4 amounts, which cause a rise in Blimp-1, both crucial transcription elements in plasma cell differentiation. Nevertheless, despite higher degrees of these canonical plasma cell protein, XBP-1-lacking B cells usually do not become plasma cells even now. This stop can be apparent not merely by having less antibody secretion, but also by reduced expression of Help (Shape 6B), an integral enzyme in course change recombination and somatic hypermutation. Therefore, at least in cells culture, XBP-1-lacking B cells show up poised to be plasma cells, however fail to do this. To analyse plasma cell development in vivo, we immunized XBP-1KO/MD4/Blimp-1-GFP mice, which communicate GFP in order from the Blimp-1 promoter to permit the unambiguous quantitation of plasma.