We investigated the expression and proinflammatory activity of interleukin (IL)-36 in patients with systemic lupus erythematosus (SLE). The expression level of IL-36, its putative receptors and the frequency of CD19⁺CD24^highCD27⁺ regulatory B (Breg) lymphocytes of peripheral blood from 43 SLE patients and 16 normal control (NC) subjects were studied using ELISA and flow cytometry. Plasma cytokines/chemokines and ex vivo productions of cytokine/chemokine from peripheral blood mononuclear cells (PBMC) stimulated with recombinant IL-36 were determined by Luminex multiplex assay. Plasma concentrations of IL-36α, IL-36γ and the proportions of circulating IL-36R-positive CD19⁺ B lymphocytes in total B lymphocytes and PBMC were significantly increased in active SLE patients compared with NC (all p < 0.05). Plasma IL-36α and IL-36γ correlated positively with SLE disease activity and elevated plasma IL-10 concentration (all p < 0.05). The frequencies of circulating Breg lymphocytes in total B lymphocytes and PBMC were significantly decreased in both inactive and active SLE patients compared with NC (all p < 0.01). The frequency of Breg lymphocytes in total B lymphocytes correlated negatively with the proportion of IL-36R-positive B lymphocytes (p < 0.05). IL-36α exerted substantial proinflammatory effect in PBMC from SLE patients by inducing the production of IL-6 and CXCL8. Upon stimulation with IL-36α and IL-36γ, ex vivo productions of IL-6 and CXCL8 were significantly increased in SLE patients compared with NC (all p < 0.05). This cross-sectional study demonstrated that over expression of circulating IL-36α may exert a proinflammatory effect as observed in human SLE.

Background: In this study, we have investigated the potential regulatory mechanisms of IL‐35 to relieve lupus nephritis (LN) through regulating Janus kinase (JAK)/signal transducers and activators of transcription (STAT) signaling pathway in mesangial cells.Results: Among 105 significant differentially expressed proteins (DEPs) between juvenile systemic lupus erythematosus (JSLE) patients with LN and healthy controls, LAIR1, PDGFRβ, VTN, EPHB4, and EPHA4 were downregulated in JSLE‐LN. They consist of an interactive network with PTPN11 and FN1, which involved in IL‐35‐related JAK/STAT signaling pathway. Besides, urinary LAIR1 was significantly correlated with JSLE‐LN clinical parameters such as SLEDAI‐2K, %CD19+ B, and %CD3+ T cells. Through bioinformatics analysis of co‐immunoprecipitation with mass spectrometry results, including GO, KEGG, and STRING, five genes interacted with Lair1 were upregulated by IL‐35, but only Myh10 was downregulated. Therefore, we presumed an interactive network among these DEPs, JAK/STAT, and IL‐35. Moreover, the downregulated phosphorylated (p)‐STAT3, p‐p38 MAPK, and p‐ERK, and the upregulated p‐JAK2/p‐STAT1/4 in IL‐35 overexpressed mesangial cells, and RNA‐sequencing results validated the potential regulatory mechanisms of IL‐35 in alleviating JSLE‐LN disease. Moreover, the relieved histopathological features of nephritis including urine protein and leukocyte scores, a decreased %CD90⁺αSMA⁺ mesangial cells and pro‐inflammatory cytokines, the inactivated JAK/STAT signals and the significant upregulated Tregs in spleen, thymus and peripheral blood were validated in Tregs and IL‐35 overexpression plasmid‐treated lupus mice.Conclusions: Our study provided a reference proteomic map of urinary biomarkers for JSLE‐LN and elucidated evidence that IL‐35 may regulate the interactive network of LAIR1‐PTPN11‐JAK‐STAT‐FN1 to affect JAK/STAT and MAPK signaling pathways to alleviate inflammation in JSLE‐LN. This finding may provide a further prospective mechanism for JSLE‐LN clinical treatment.