B cells in Crohn's patients presented reduced IL-35 expression capacity

Interleukin (IL)-35 has capacity to ameliorate experimental colitis and is upregulated in immune cells from active Crohn's disease (CD) patients. Nonetheless, CD continues to be an incurable disease with characteristics of chronic relapsing-remitting inflammation. In this study, we investigated the production of IL-35 by B cells from active CD patients and non-CD controls. Immediately ex vivo, the mRNA transcription of IL-12/IL-35 subunit IL12A was significantly higher in CD B cells than in control B cells, and the mRNA transcription of IL-27/IL-35 subunit EBI3 was significantly higher in mild CD and moderate CD B cells than in control B cells. However, we also found that CpG-activated B cells and BCR + CD40-activated B cells from CD subjects presented significantly lower IL12A and lower EBI3 transcription than their counterparts from control subjects. We further evaluated IL-35 protein secretion and confirmed that B cell-mediated IL-35 protein secretion was lower in CD patients than in controls. However, IL-35-Fc preconditioning was able to significantly increase IL-35 production from B cells and to eliminate the difference in IL-35 production capacity between controls and CD patients. Furthermore, these IL-35-Fc-preconditioned B cells were able to suppress IFN-γ and IL-17 production from CD4⁺CD25^- T cells more potently than Fc control-preconditioned B cells. Rh IL-27Rα-Fc, a soluble form of B cell-specific IL-35 receptor, significantly increased IFN-γ and IL-17 production. Together, these data supported a role of B cell-mediated IL-35 in suppressing IFN-γ and IL-17 inflammation. However, despite the fact that CD B cells presented higher transcription of IL-35 subunits directly ex vivo, CD B cells also presented reduced capacity for further IL-35 production upon activation.