Macrophage migration inhibitory factor (MIF) plays a pivotal role in the inflammatory response in endotoxemia and in the delayed-type hypersensitivity response, but its potential as a regulator of immunologically induced disease is unknown. We have addressed this issue by administering a neutralizing anti-MIF antibody in a rat model of immunologically induced crescentic anti-glomerular basement membrane (GBM) glomerulonephritis. Six individual experiments using paired inbred littermates were performed. Rats were primed with rabbit immunoglobulin on day −5 and then injection with rabbit anti–rat GBM serum on day 0. Pairs of animals were treated with anti-MIF or a control monoclonal antibody from the time of anti-GBM serum administration until being killed 14 d later. Control antibody-treated animals developed severe proteinuria and renal function impairment with severe histological damage due to marked leukocytic infiltration and activation within the kidney. In contrast, anti-MIF treatment substantially reduced proteinuria, prevented the loss of renal function, significantly reduced histological damage including glomerular crescent formation, and substantially inhibited renal leukocytic infiltration and activation (all P <0.001 compared with control treatment). Inhibition of renal disease by anti-MIF treatment was attributed to preventing the marked upregulation of interleukin-1β, leukocyte adhesion molecules including intercellular adhesion molecule-1 and vascular cell adhesion molecule-1, and inducible nitric oxide synthase expression seen in the control antibody-treated animals. This inhibition of progressive renal injury was mirrored by the complete suppression of the skin delayed-type hypersensitivity response to the challenge antigen (rabbit IgG). Interestingly, anti-MIF treatment did not effect the secondary antibody response or immune deposition within the kidney, indicating that MIF participates in cellular-based immunity in this primed macrophage-dependent anti-GBM glomerulonephritis. In conclusion, this study has demonstrated a key regulatory role for MIF in the pathogenesis of immunologically induced kidney disease. These results argue that blocking MIF activity may be of benefit in the treatment of human rapidly progressive glomerulonephritis, and suggest that MIF may be important in immune-mediated disease generally.

Summary Nucleotide‐binding, oligomerization domain (NOD)‐like receptor family, pyrin domain containing 3 (NLRP3) gene polymorphism was reported to be associated with susceptibility, disease activity or anti‐tumour necrosis factor (TNF) treatment response in rheumatoid arthritis (RA). However, the roles of NLRP3 inflammasome in the development of RA have not yet been elucidated fully. The present study aimed to study the role of NLRP3 inflammasome in RA. NLRP3 inflammasome activation in synovial tissues from RA and osteoarthritis (OA) patients were assessed by Western blot. Active caspase‐1 in synovia was stained by a FAM‐FLICA caspase‐1 probe. Mice with collagen‐induced arthritis (CIA) were treated with MCC950, a selective NLRP3 inhibitor, or vehicle for 2 weeks. The clinical score of arthritis, synovial inflammation and cartilage erosion were assessed. Proinflammatory cytokines were measured by enzyme‐linked immunosorbent assay (ELISA). The results showed that NLRP3 inflammasome was highly activated in both synovia from RA patients and CIA mice. Activation of NLRP3 inflammasome occurred mainly in the infiltrating monocyte/macrophages in synovia, but not in fibroblast‐like synoviocytes. Treatment with MCC950 resulted in significantly less severe joints inflammation and bone destruction. NLRP3 inflammasome activation in the synovia was inhibited significantly by MCC950 with reduced production of interleukin (IL)‐1β. The inhibition of NLRP3 inflammasome activation by MCC950 was confirmed further in a human monocytic cell line, THP‐1. In conclusion, NLRP3 inflammasome is involved in the pathogenesis of RA. Targeting NLRP3 inflammasome with a small molecule inhibitor might be a novel therapeutic strategy for RA.

Objective The NLRP3 inflammasome plays key roles in inflammation and autoimmunity, and puriner-gic receptor P2X7 has been proposed to be upstream of NLRP3 activation. The aim of the present study, using murine models, was to investigate whether the P2X7/ NLRP3 inflammasome pathway contributes to the pathogenesis of lupus nephritis (LN). Methods MRL/lpr mice were treated with the selective P2X7 antagonist brilliant blue G (BBG) for 8 weeks. Following treatment, the severity of renal lesions, production of anti-double-stranded DNA (anti-dsDNA) antibodies, rate of survival, activation of the NLRP3/ ASC/caspase 1 inflammasome pathway, and ratio of Thl7 cells to Treg cells were evaluated. P2X7-targeted small interfering RNA (siRNA) was also used for in vivo intervention. Similar evaluations were carried out in NZM2328 mice, a model of LN in which the disease was accelerated by administration of adenovirus-expressing interferon-α (AdIFNα). Results Significant up-regulation of P2X7/NLRP3 inflammasome signaling molecules was detected in the kidneys of MLR/lpr mice as compared with normal control mice. Blockade of P2X7 activation by BBG suppressed NLRP3/ASC/caspase 1 assembly and the subsequent release of interleukin-1β (IL-1β), resulting in a significant reduction in the severity of nephritis and circulating anti-dsDNA antibodies. The lifespan of the treated mice was significantly prolonged. BBG treatment reduced the serum levels of IL-1β and IL-17 and the Thl7:Treg cell ratio. Similar results were obtained by specific siRNA silencing of P2X7 in vivo. The effectiveness of BBG treatment in modulating LN was confirmed in NZM2328 mice with AdIFNα-accelerated disease. Conclusion Activation of the P2X7 signaling pathway accelerates murine LN by activating the NLRP3/ASC/caspase 1 inflammasome, resulting in increased IL-1β production and enhanced Thl7 cell polarization. Thus, targeting of the P2X7/NLRP3 pathway should be considered as a novel therapeutic strategy in patients with lupus.

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Follicular T regulatory (Tfr) cells inhibit follicular T helper (Tfh) cells mediated B cell responses. Tfh cells are involved in the pathogenesis of systemic lupus erythematosus (SLE). However, the role of Tfr cells in SLE remains unclear. The frequency of circulating Tfr and Tfh cells were examined in SLE patients and healthy controls. The frequency of circulating Tfr cell decreased and Tfh/Tfr ratio increased in SLE patients. Serum anti-dsDNA antibody level positively correlated with frequency of Tfh cells and Tfh/Tfr ratios but negatively correlated with the frequency of Tfr cells. Moreover, the frequency of Tfr and Tfh/Tfr ratio but not that of Tfh was correlated with diseases activity. In addition, increase in Tfr cell numbers and decrease in the Tfh/Tfr ratios were observed with successful treatments. Thus, Tfr cells should be considered as a biomarker for SLE and their role in the pathogenesis of SLE warrants further investigation.

Objective Development of proteinuria in lupus nephritis (LN) is associated with podocyte dysfunction. The NLRP3 inflammasome has been implicated in the pathogenesis of LN. This study investigates whether NLRP3 inflammasome activation is involved in the development of podocyte injury in LN. Methods A fluorescence-labeled caspase-1 inhibitor probe was used to detect the activation of NLRP3 inflammasomes in podocytes in lupus-prone NZM2328 mice and in renal biopsies from LN patients. MCC950, a selective inhibitor of NLRP3, was used to treat NZM2328 mice. Proteinuria, ultrastructure of podocytes and renal pathology were evaluated. In vitro, sera from diseased NZM2328 mice were used to stimulate a podocyte cell line and cells were subjected to flow cytometry analysis. Results NLRP3 inflammasomes were activated in podocytes of lupus-prone mice and LN patients. Inhibition of NLRP3 with MCC950 ameliorated proteinuria, renal histological lesions and podocyte foot process effacement in lupus-prone mice. In vitro, sera from NZM2328 diseased mice activated NLRP3 inflammasomes in the podocyte cell line through reactive oxygen species (ROS) production. Conclusion NLRP3 inflammasomes were activated in podocytes of both LN patients and in lupus-prone mice. Activation of NLRP3 is involved in the pathogenesis of podocyte injuries and the development of proteinuria in LN.

This study demonstrates that macrophage proliferation is a feature of the more aggressive forms of human GN. Local proliferation may be an important mechanism for amplifying macrophage-mediated renal injury. In addition, the degree of local macrophage proliferation may be a useful diagnostic and prognostic indicator for human GN.

Myeloid-derived suppressor cells (MDSC) and Th17 cells were found to expand in collagen-induced arthritis (CIA) significantly. Two subsets of MDSC, polymorphonuclear (PMN) and mononuclear (MO), were detected and their ratios varied during the development of CIA. The depletion of MDSC in vivo resulted in suppression of T-cell proliferation and decreased IL-17A and IL-1β production. The adoptive transfer of MDSC restored the severity of arthritis and Th17 cell differentiation. The depletion of MDSCs on day 35 resulted in arthritis amelioration without reaching a significant difference. Furthermore, MDSCs from CIA mice had higher production of IL-1β and promoted Th17 cell differentiation. The expansion of MDSCs in the peripheral blood of rheumatoid arthritis (RA) patients was in correlation with increased Th17 cells and disease activity DAS28. These results support the hypothesis that MDSC may play a significant proinflammatory role in the pathogenesis of CIA and RA by inducing Th17 development in an IL-1β-dependent manner.