Interestingly, there is some evidence describing the conversion of murine CD4+CD25+FOXP3+ Treg cells into CD4+CD25+FOXP3- T cells as a result of FOXP3 downregulation, thus subverting Tregs to T effector and predisposing autoimmunity [34, 35]. Indeed, chronic inflammation seen in CVID disease might create a milieu in which activation

of effector T cells may cause downregulation of FOXP3 via production of inflammatory cytokines, thus alter Tregs’ proportions and consequently increase the risk of autoimmunity [17]. However, more studies are needed to support this idea. Our findings in this study indicate that both CTLA-4 and GITR mRNA levels are decreased in CVID patients compared to the control group. This is the first time that

CTLA-4 and GITR genes are evaluated at mRNA level in CVID patients. Only one study JAK inhibitor by Yu et al. showed that the GITR molecule expression is attenuated at protein level (using MFI by flow cytometric analysis) in CD4+CD25highCD127low Tregs from CVID patients with autoimmunity comparing those without autoimmunity and also healthy BGB324 controls [21]. Several mechanisms for Tregs-mediated immune suppression have been described in which both surface markers (e.g. CTLA-4, GITR, LAG-3) and soluble cytokines (e.g. IL-10, TGF-β and IL-35) have been implicated [8-10]. However, the role of soluble factors is still controversial and cell–cell contact has also been

considered as a major aetiology [8-10]. The CTLA-4 and GITR molecules are constitutively expressed at high levels on Tregs’ surfaces. The main role of CTLA-4 molecule is to compete with CD28 molecule for CD80/CD86 markers on dendritic cells (DCs) and thus restraining the effector T cell activation [8, 36]. Negative signal transduction of Tregs by CTLA-4 to DCs can convert them to tolerogenic DCs [37]. During the effector phase of an immune response, the GITR molecule promotes Tregs’ activation and proliferation, which restrict uncontrolled immune cell activation [38, 39]. Hence, it is possible that changes in CTLA-4 and GITR expression together with downregulation of FOXP3 protein might MYO10 account for Tregs’ dysfunction observed in CVID patients. It is possible that ICOS has the same costimulatory role in Treg activation (like conventional T cells) and genetic defect in ICOS gene has been reported to be associated with susceptibility to CVID and defective Treg function [40]. Therefore, evaluating the expression of ICOS might provide additional data in pathogenesis of CVID and should be considered in future studies. Furthermore, recent study reported that Th17 populations differentiated in vitro from natural naive FOXP3+ Tregs, which should be investigated in another study via evaluation of IL-17-producing cells in CVID patients [41].