Candida induces EBI3 expression to suppress IL-12p70 production by DC

Candida albicans is normally a harmless commensal fungus of humans with up to 85% of individuals colonised by this organism at mucosal sites without detriment to health. In such individuals, a balance clearly exists between immune response and tolerance. Dendritic cells (DCs) control host immune response or non-responses through cytokine signals. Both IL-12 and IL-35 are heterodimeric cytokines produced by DCs and share a common protein subunit (p35). The cytokine IL-12p70 is a functional heterodimeric cytokine consisting of p40 and p35 and directs Th1 responses, while IL-35 consists of EBI3 and p35 and induces regulatory T-cells and suppression of Th1 and Th17 responses. Suppressing IL-12p70 and enhancing IL-35 production in DCs would effectively turn the host immune response to tolerance. We hypothesise that a tolerogenic DC phenotype partially contributes through higher EBI3 expression to reduce IL-12p70 secretion by competitive IL-12p35 binding. Objective: The aim of this study was to investigate C. albicans mediated suppression of IL-12p70 production in DCs and examine the molecular basis of this. Methods: Mouse bone marrow DCs (BMDCs) were challenged with heat killed C. albicans (HKC). In some experiments, LPS stimulation was incorporated. Real time (RT)-PCR, ELISA and Western blot (WB) including immunoprecipitation Western blot (IP-WB) were used to detect EBI3, p35 and p40 expression. Chinese Hamster Ovary (CHO) clone with biscistronic expression of IL-12p40 and p35 followed by transfection with EBI3. Results: 1) Differential expression of EBI3, IL-12p35 and p40 was stimulated by C. albicans and LPS. 2) HKC suppressed LPS induced IL-12p70 expression in BMDC. 3) Over-expression of EBI3 resulted in significant inhibition of IL-12p70 secretion in CHO clones with IL-12p70 expression. 4) C. albicans induced a high IL-10 expression in BMDC. Conclusion: Candida albicans induces tolerogenic DC by stimulating EBI3 expression for IL-35 production to suppress IL-12p70 production.