TACI expression and plasma cell differentiation are impaired in the absence of functional IκBNS

Abstract

Impaired classical NF‐κB pathway signaling causes reduced antibody responses to T‐independent (TI) antigens. We investigated the potential reasons for defective TI responses in mice lacking the atypical inhibitory kappa B (IκB) protein of the NF‐κB pathway, IκBNS. Analyses of the plasma cell compartment in vitro and in vivo after challenge with lipopolysaccharide (LPS) showed significant decreases in the frequencies of plasma cells in the absence of IκBNS. In vitro activation of B cells via the B cell receptor or via Toll‐like receptor 4 revealed that early activation events were unaffected in IκBNS‐deficient B cells, while proliferation was reduced compared to in similarly stimulated wildtype (wt) B cells. IκBNS‐deficient B cells also displayed impaired upregulation of the transmembrane activator and calcium modulator cyclophilin ligand interactor (TACI), which is essential for TI responses, and decreased sensitivity to TACI ligands upon stimulation. Furthermore, IκBNS‐deficient B cells, in contrast to wt B cells, displayed altered expression of IRF4, Blimp‐1 and Pax5 upon LPS‐induced differentiation, indicating impaired transcriptional regulation of plasma cell generation.

Nfkbidis required for immunity and antibody responses toToxoplasma gondii

“…Previous work has shown that Nfkbid null mice completely fail to develop B-1 cells, lack circulating IgM and IgG3 antibodies, and cannot respond to T-independent (T-I) type II antigens such as NP-ficoll [31–33]. IκBNS also promotes early plasma blast differentiation [34] and IgG1 responses to model T-dependent antigens [RW.ERROR - Unable to find reference:doc:6096c5808f080d3356fb1a6a], enhances T cell production of IL-2 and IFNγ [35], supports development of T regulatory cells [36] and suppresses TLR-induced cytokine expression in macrophages [37]. The tetraspanin, Tspan8, is within the chr10 QTL (Mb 115.8-116.2) and is the most highly polymorphic gene between A/J and C57BL/6J mice in this region (Dataset S1).…”

“…To further validate these findings, frequencies of class switched IgM-IgD-CD5+ (B-1a) or CD5-(B-1b) cells within the CD43+ B-1 cell compartments of the peritoneum (not shown) and spleen were determined, and a similar trend was observed (Fig 6C). Following infection, B-1 cells in the spleens of A/J mice maintained high levels of BAFFR and TACI expression and expressed higher levels of surface CD138 relative to C57BL/6J mice (Fig 6D-E), markers known to be induced by Nfkbid and important for B cell activation and differentiation into antibody secreting cells [34]. In addition to differences in humoral immunity, an increase in peritoneal CD8 T cell in vitro recall production of IFNγ was noted in A/J relative to C57BL/6J mice, however other parameters, including granzyme B and IL-2 expression and CD4 T cell responses were similar (Fig S6).…”

“…Though the exact pathway remains to be investigated, Nfkbid is downstream of TLR signaling in B cells [31,32,34], which in B-1a cells causes them to downregulate CD5 and facilitate differentiation into antibody secreting cells [44, 54]. CD5 is a potent negative regulator of antigen receptor signaling that renders B-1a cells unresponsive to B cell receptor (BCR)-triggering.…”

“…In these situations, resistant A/J mice often had two-fold greater percentages of IgM-IgD-B-1 cells relative to the susceptible C57BL/6 mice. Following infection, B-1 cells in the spleens of A/J mice maintained high levels of BAFFR and TACI expression and expressed higher levels of surface CD138 relative to C57BL/6J mice ( Fig 5E), markers known to be induced by Nfkbid and important for B cell activation and differentiation into antibody secreting cells (66). The B-2 compartment of A/J also showed enhanced activation.…”

“…The ability of B-1 cells to make parasite-specific antibodies, though of lower affinity, potentially amplifies B-2 immune responses to T. gondii through internalization of B-1 cell-derived antigen-antibody complexes (72), assisting MHCIIantigen presentation for CD4 T cell help(73). Moreover, the effect of B cell-mediated immunity to T. gondii and other pathogens is likely underestimated in murine models using the C57BL/6 background, as enhanced B-1 and B-2 responses were primarily observed in A/J mice.Though the exact pathway remains to be investigated, Nfkbid is downstream of TLR signaling in B cells(48,49,66), which in B-1a cells causes them to downregulate CD5 and facilitate differentiation into antibody secreting cells(60,74). CD5 is a potent negative regulator of antigen receptor signaling that renders B-1a cells unresponsive to B cell receptor (BCR)-triggering(75).…”