T-helper 17 cell cytokines and interferon type I: partners in crime in systemic lupus erythematosus?

Introduction: A hallmark of systemic autoimmune diseases like systemic lupus erythematosus (SLE) is the increased expression of interferon (IFN) type I inducible genes, so-called IFN type I signature. Recently, T-helper 17 subset (Th17 cells), which produces IL-17A, IL-17F, IL-21, and IL-22, has been implicated in SLE. As CCR6 enriches for Th17 cells, we used this approach to investigate whether CCR6(+) memory T-helper cells producing IL-17A, IL-17F, IL-21, and/or IL-22 are increased in SLE patients and whether this increase is related to the presence of IFN type I signature. Methods: In total, 25 SLE patients and 15 healthy controls (HCs) were included. SLE patients were divided into IFN type I signature-positive (IFN+) (n = 16) and negative (IFN-) (n = 9) patients, as assessed by mRNA expression of IFN-inducible genes (IFIGs) in monocytes. Expression of IL-17A, IL-17F, IL-21, and IL-22 by CD4(+) CD45RO(+) CCR6(+) T cells (CCR6(+) cells) was measured with flow cytometry and compared between IFN+, IFN-patients and HCs. Results: Increased percentages of IL-17A and IL-17A/IL-17F double-producing CCR6(+) cells were observed in IFN+ patients compared with IFN-patients and HCs. IL-17A and IL-17F expression within CCR6(+) cells correlated significantly with IFIG expression. In addition, we found significant correlation between B-cell activating factor of the tumor necrosis family (BAFF)-a factor strongly correlating with IFN type I - and IL-21 producing CCR6(+) cells. Conclusions: We show for the first time higher percentages of IL-17A and IL-17A/IL-17F double-producing CCR6(+) memory T-helper cells in IFN+ SLE patients, supporting the hypothesis that IFN type I co-acts with Th17 cytokines in SLE pathogenesis.