IL-21 secreting cTfh cells were higher in MS patients
Aberrant secretion of inflammatory cytokines plays an important role in autoimmune disease. We evaluated some signature cytokines, such as IFN-γ, IL-4, IL-17 and IL-21. Our data indicate that the frequency of IL-21 secreting PBMCs were significantly higher in MS patients than those in HC (2.62±0.34% vs. 0.93±0.33%, p=0.0004) (Fig. 3a,c), whereas no significant difference was observed in IFN-γ, IL-4 and IL-17 production between MS patients and HC (Fig. S1). The frequency of IL-21 secreting CD3+ T cells was higher in MS patients compared to HC (1.95±0.32% vs. 0.81±0.49%, p=0.0009) (Fig. 3c), whereas no significant differences in the frequencies of IL-21 producing B cells and monocytes were observed between MS patients and HC (data not shown). Comparative analysis of IL-21 secretion by CD4+ T cells and CD8+ T cells showed that significantly higher percentage of CD4+ T cells secreted IL-21 in MS patients compared to HC (2.32±0.23% vs. 0.9±0.41%, p=0.002), while IL-21 producing CD8+ T cells showed no significant difference between HC and MS patients (Fig. 3b, c).
Next, we analyzed the secretion of cytokines by cTfh cells and compared their frequencies between MS patients and HC. The frequency of IL-21 secreting cTfh cells was remarkably higher in MS patients compared to HC (8.83±1.29% vs. 3.53±1.25%, p=0.003) (Fig. 3d, e), whereas no significant difference was observed in IFN-γ, IL-4 and IL-17 secreting cTfh cells between MS patients and HC (Fig. S2). Comparative analysis of IL-21 production by follicular vs. non-follicular Th cells revealed that, higher percentage of cTfh cells secreted IL-21 compared to their counterpart non-follicular Th cells in both HC (3.53±1.25% vs. 1.66±0.64%, p=0.06) and MS (8.83±1.29% vs. 1.35±0.25%, p<0.0001). Interestingly, IL-21 secreting cTfh cells was significantly higher in MS compared to HC (Fig. 3d,e). Collectively, these findings suggest that cTfh cells may engage with elevated secretion of IL-21 in MS patients over other immune cells.