Abstract
IL-38 is a newly identified cytokine that belongs to the IL-1 family. In our previous study, we found elevated plasma levels of IL-38 in patients with systemic lupus erythematosus (SLE). However, the clear relationship of IL-38 expression in plasma, peripheral blood mononuclear cells (PBMCs) and clinical and laboratory features needs elucidation. Additionally, we evaluated the possible role of IL-38 in regulating production of inflammatory cytokines in PBMCs in vitro. A pristane-induced murine lupus model was used to further demonstrate the effects of IL-38 on cytokines in vivo and discuss the significance of IL-38 in lupus development. The results showed that mRNA expression of IL-38 in PBMCs of patients with SLE was elevated compared with volunteers, and expression of IL-38 in both plasma and PBMCs was strongly related to clinical features, such as haematuria and proteinuria, and correlated with a SLEDAI score. Plasma levels of TNF-α, IL-1β, IL-6 and IL-23 were elevated in patients with SLE and were related to plasma levels of IL-38. In vitro, PBMCs of patients with SLE stimulated with IL-38 showed a decreased expression of the four inflammatory cytokines compared with PBMCs of patients without treatment. Interestingly, IL-38 administration in lupus mice significantly reduced the development of lupus, such as reduced proteinuria, improved histological examinations of the kidneys and down-regulated inflammatory cytokines. In conclusion, IL-38 may suppress synthesis of pro-inflammatory cytokines and therefore regulate lupus pathogenesis.