[Show abstract][Hide abstract] ABSTRACT: The generation of robust T-cell-dependent humoral immune responses requires the formation and expansion of germinal center
structures within the follicular regions of the secondary lymphoid tissues. B-cell proliferation in the germinal center drives
ongoing antigen-dependent selection and the generation of high-affinity class-switched plasma and memory B cells. However,
the mechanisms regulating B-cell proliferation within this microenvironment are largely unknown. Here, we report that cyclin
D3 is uniquely required for germinal center progression. Ccnd3−/− mice exhibit a B-cell-intrinsic defect in germinal center maturation and fail to generate an affinity-matured IgG response.
We determined that the defect resulted from failed proliferative expansion of GL7+ IgD− PNA+ B cells. Mechanistically, sustained expression of cyclin D3 was found to be regulated at the level of protein stability and
controlled by glycogen synthase kinase 3 in a cyclic AMP-protein kinase A-dependent manner. The specific defect in proliferative
expansion of GL7+ IgD− PNA+ B cells in Ccnd3−/− mice defines an underappreciated step in germinal center progression and solidifies a role for cyclin D3 in the immune response,
and as a potential therapeutic target for germinal center-derived B-cell malignancies.
Full-text · Article · Oct 2010 · Molecular and Cellular Biology
[Show abstract][Hide abstract] ABSTRACT: The marginal zone is a cellular niche bordering the marginal sinus of the spleen that contains specialized B-cell and macrophage subsets poised to capture bloodborne antigens. Marginal zone B cells are retained in this niche by integrin-mediated signaling induced by G protein-coupled receptors (GPCRs) and, likely, the B-cell receptor (BCR). Sphingosine-1-phosphate (S1P) signaling via the S1P family of GPCRs is known to be essential for B-cell localization in the marginal zone, but little is known about the downstream signaling events involved. Here, we demonstrate that the adaptor protein SHEP1 is required for marginal zone B-cell maturation. SHEP1 functions in concert with the scaffolding protein CasL, because we show that SHEP1 and CasL are constitutively associated in B cells. SHEP1 association is required for the BCR or S1P receptor(s) to induce the conversion of CasL into its serine/threonine hyperphosphorylated form, which is important for lymphocyte adhesion and motility. Thus, SHEP1 orchestrates marginal zone B-cell movement and retention as a key downstream effector of the BCR and S1P receptors.
Full-text · Article · Oct 2010 · Proceedings of the National Academy of Sciences
[Show abstract][Hide abstract] ABSTRACT: B. anthracis is the causative agent of anthrax. Pathogenesis is primarily mediated through the exotoxins lethal factor and edema factor, which bind protective antigen (PA) to gain entry into the host cell. The current anthrax vaccine (AVA, Biothrax) consists of aluminum-adsorbed cell-free filtrates of unencapsulated B. anthracis, wherein PA is thought to be the principle target of neutralization. In this study, we evaluated the efficacy of the natural adjuvant, C3d, versus alum in eliciting an anti-PA humoral response and found that C3d conjugation to PA and emulsion in incomplete Freund's adjuvant (IFA) imparted superior protection from anthrax challenge relative to PA in IFA or PA adsorbed to alum. Relative to alum-PA, immunization of mice with C3d-PA/IFA augmented both the onset and sustained production of PA-specific antibodies, including neutralizing antibodies to the receptor-binding portion (domain 4) of PA. C3d-PA/IFA was efficacious when administered either i.p. or s.c., and in adolescent mice lacking a fully mature B cell compartment. Induction of PA-specific antibodies by C3d-PA/IFA correlated with increased efficiency of germinal center formation and plasma cell generation. Importantly, C3d-PA immunization effectively protected mice from intranasal challenge with B. anthracis spores, and was approximately 10-fold more effective than alum-PA immunization or PA/IFA based on dose challenge. These data suggest that incorporation of C3d as an adjuvant may overcome shortcomings of the currently licensed aluminum-based vaccine, and may confer protection in the early days following acute anthrax exposure.