Kim et al. identify an autoinflammatory disease in mice that is driven by IL-18, resulting from an inactivating mutation in the actin-depolymerizing cofactor Wdr1. This alteration in actin dynamics is recognized by the pyrin inflammasome and results in exaggerated monocyte IL-18 production, whereas inflammasome activation in mature macrophages is unaltered.

Anti-microbial signaling pathways are normally triggered by innate immune receptors when detecting pathogenic microbes to provide protective immunity. Here we show that the inflammasome sensor Nlrp1 aggravates DSS-induced experimental mouse colitis by limiting beneficial, butyrate-producing Clostridiales in the gut. The colitis-protective effects of Nlrp1 deficiency are thus reversed by vancomycin treatment, but recapitulated with butyrate supplementation in wild-type mice. Moreover, an activating mutation in Nlrp1a increases IL-18 and IFNγ production, and decreases colonic butyrate to exacerbate colitis. We also show that, in patients with ulcerative colitis, increased NLRP1 in inflamed regions of the colon is associated with increased IFN-γ. In this context, NLRP1, IL-18 or IFN-γ expression negatively correlates with the abundance of Clostridiales in human rectal mucosal biopsies. Our data identify the NLRP1 inflammasome to be a key negative regulator of protective, butyrate-producing commensals, which therefore promotes inflammatory bowel disease.

Background: Acute rheumatic fever (ARF) and rheumatic heart disease are autoimmune consequences of group A streptococcus infection and remain major causes of cardiovascular morbidity and mortality around the world. Improved treatment has been stymied by gaps in understanding key steps in the immunopathogenesis of ARF and rheumatic heart disease. This study aimed to identify (1) effector T cell cytokine(s) that might be dysregulated in the autoimmune response of patients with ARF by group A streptococcus, and (2) an immunomodulatory agent that suppresses this response and could be clinically translatable to high-risk patients with ARF. Methods: The immune response to group A streptococcus was analyzed in peripheral blood mononuclear cells from an Australian Aboriginal ARF cohort by a combination of multiplex cytokine array, flow cytometric analysis, and global gene expression analysis by RNA sequencing. The immunomodulatory drug hydroxychloroquine was tested for effects on this response. Results: We found a dysregulated interleukin-1β-granulocyte-macrophage colony-stimulating factor (GM-CSF) cytokine axis in ARF peripheral blood mononuclear cells exposed to group A streptococcus in vitro, whereby persistent interleukin-1β production is coupled to overproduction of GM-CSF and selective expansion of CXCR3 + CCR4 − CCR6 − CD4 T cells. CXCR3 + CCR4 − CCR6 − CD4 T cells are the major source of GM-CSF in human CD4 T cells and CXCL10, a CXCR3 ligand and potent T helper 1 chemoattractant, was elevated in sera from patients with ARF. GM-CSF has recently emerged as a key T cell-derived effector cytokine in numerous autoimmune diseases, including myocarditis, and the production of CXCL10 may explain selective trafficking of these cells to the heart. We provide evidence that interleukin-1β amplifies the expansion of GM-CSF-expressing CD4 T cells, which is effectively suppressed by hydroxychloroquine. RNA sequencing showed shifts in gene expression profiles and differentially expressed genes in peripheral blood mononuclear cells derived from patients at different clinical stages of ARF. Conclusions: Given the safety profile of hydroxychloroquine and its clinical pedigree in treating autoimmune diseases such as rheumatoid arthritis, where GM-CSF plays a pivotal role, we propose that hydroxychloroquine could be repurposed to reduce the risk of rheumatic heart disease after ARF.

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In addition to several other extracellular substances, phagocytosis of amyloid-forming peptides can perturb cellular homeostasis, leading to activation of the cytoplasmic innate immune receptor NLRP3. Once triggered, NLRP3 forms an inflammasome complex that ultimately cleaves pro-IL-1β and pro-IL-18 into their mature, secreted forms. Here we describe a protocol by which one type of amyloidogenic peptide, islet amyloid polypeptide (IAPP, otherwise known as amylin) can be prepared and used to stimulate myeloid cells in vitro to engage the NLRP3 inflammasome. Methods for measuring the ensuing inflammasome activation are also described. Although initially soluble, IAPP monomers rapidly aggregate in solution to form oligomers and subsequently insoluble amyloid fibrils. More work is required to examine how this transition influences inflammasome activation for different types of amyloid. The course of amyloid formation and corresponding inflammatory capacity of these pre-fibrillar species following uptake also requires further examination, and we hope that our protocols are useful in these endeavors. While these protocols are restricted to examination of synthetic IAPP, isolation of IAPP aggregates from human and transgenic mouse pancreas will be required to definitively determine the proinflammatory effects of endogenous IAPP oligomers and fibrils.

HighlightsHCQ inhibits proliferation of human CD4 T-cells without affecting early activation HCQ dysregulates mitochondrial superoxide production in activated CD4 T-cells Dysregulated ROS impairs autophagic flux in activated CD4 T-cells HCQ limits antigenspecific T cell responses in patients with celiac disease ex vivo

Hydroxychloroquine (HCQ) is a widely used and effective immunomodulatory drug. HCQ can cause dose-related retinal damage, thought to be due to inhibitory effects on lysosomes and autophagy. Using a human retinal pigment epithelial cell line (ARPE-19 cells), we confirm HCQ's inhibitory effect on autophagy and report that it inhibits mTORC1-mediated cholesterol biosynthesis. Cellular cholesterol content regulates lysosomal membrane permeability and thereby influences sensitivity to cell death. Cellular cholesterol insufficiency renders ARPE-19 cells more susceptible to a critical environmental threat, namely UV-induced cell death. We also show that HCQ induces apoptosis-independent disruption of phospholipid asymmetry, whereby caspase-independent phosphatidylserine (PS) exposure is mediated by cytosolic cathepsin B. HCQ-induced, caspase-independent PS exposure was inhibitable by the neutral pH-selective cathepsin B inhibitor Z-Arg-Lys-AOMK and was amplified by cholesterol lowering (simvastatin) and depleting (methyl-beta cyclodextrin) agents. We therefore conclude that HCQ also induces the release of lysosomal cathepsin B into the cytosol in response to lysosomal membrane permeability caused by cellular cholesterol insufficiency. We suggest that restricting UV exposure and avoiding cholesterol-lowering agents in combination with long term administration of HCQ might offer preventative strategies to protect against HCQ-induced retinal degeneration. We also provide evidence that neutral pH-selective cathepsin B inhibitors could represent a novel approach to treatment. Our findings may have broader implications for the prevention of retinal cell death and preservation of vision.

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