Immature and mature naive B cell success is differently promoted by Bcl-XL and Bcl-2, respectively, in mice24

Immature and mature naive B cell success is differently promoted by Bcl-XL and Bcl-2, respectively, in mice24. cell differentiation to memory and antibody-secreting B cells. The defective functionality of CVID patients B cells could be the consequence of alterations in apoptosis regulation. We studied the balance KIAA0078 of Bcl-2 family anti-/pro-apoptotic proteins to identify molecular Ginkgolide B mechanisms that could underlie B cell survival defects in CVID. We used flow cytometry to investigate Bcl-2, Bcl-XL, Bax, and Bim expression in B cells ex vivo and after anti-CD40 or anti-BCR activation with or without IL-21, besides to spontaneous and stimulation-induced Caspase-3 activation and viable/apoptotic B cell subpopulations. We found increased basal levels of Bax and Bim in CVID B cells that correlated with low viability and high Caspase-3 activation only in CD27+ B cells, particularly in a subgroup of apoptosis-prone CVID (AP-CVID) patients with low peripheral B cell counts and high autoimmunity prevalence (mostly cytopenias). We detected a broad B cell defect in CVID regarding Bcl-2 and Bcl-XL induction, irrespective of the stimulus used. Therefore, peripheral CVID memory B cells are prompted to die from apoptosis due to a constitutive Bcl-2 family protein imbalance and defective protection from activation-induced apoptosis. Interestingly, anti-CD40 and IL-21 induced normal and even higher levels of Bcl-XL, respectively, in CD27+ B cells from AP-CVID, which was accompanied Ginkgolide B by cell viability increase. Thus low-survival memory B cells from AP-CVID can overcome their cell death regulation defects through pro-survival signals provided by T cells. In conclusion, we identify apoptosis regulation defects as disease-contributing factors in CVID. B cell counts and case history of cytopenias might be useful to predict positive responses to therapeutic approaches targeting T-dependent signaling pathways. Introduction Common variable immunodeficiency Ginkgolide B (CVID) is the commonest symptomatic primary humoral immunodeficiency, characterized by hypogammaglobulinemia and poor response to vaccination. CVID patients not only suffer from respiratory and/or gut recurrent infections but also additional noninfectious features, including autoimmune and autoinflammatory processes or lymphoproliferative disorders. Patients benefit from substitutive gammaglobulin therapy1C3. Although many immunological defects have been described in CVID, pathogenesis of the disease remains unknown4. An abnormal late B cell differentiation to memory B cells and antibody-secreting cells (ASC) is usually a consistent CVID finding. Accordingly, patients have been classified depending on naive, non-switched and switched memory B cell numbers5C7. The generation of memory B cells and ASC is crucial to establish humoral immune responses. T cell cooperation is essential and occurs through contact between T cell membrane molecules and corresponding B cell ligands8, whose relevance has been exemplified by naturally occurring immunodeficiencies9. Secretion of cytokines like interleukin (IL)-21, mainly produced by activated follicular T cells, also instructs B cell differentiation10C13. Apart from their effect on proliferation and differentiation, these stimuli also influence apoptosis/survival balance needed to preserve B cell homeostasis, which shows specific requirements depending on B cell maturation and activation status. Activation threshold required for B cell differentiation is usually significantly lower while apoptosis susceptibility is usually higher in memory compared to naive B cells14,15. IL-21 co-stimulation is essential in human B cell differentiation to ASC, but T cell conversation is usually mandatory16. Thus B cell receptor (BCR) activation induces B cell apoptosis, even enhanced by IL-21, if survival signals provided through CD40 contact are absent. Accordingly, the stimulatory/inhibitory effect of IL-21 depends on the Ginkgolide B accompanying signal and the B cell subpopulation evaluated17,18. We previously exhibited that memory B cell loss in a CVID patients subgroup (with compromised memory B cell compartment) could be the consequence of increased susceptibility to activation-induced apoptosis15. Moreover, several studies reported that CVID subgroups can be distinguished depending on B cell functionality in vitro19,20 that may.