Summary
Ancient organisms have a combined coagulation and immune system, and although links between inflammation and hemostasis exist in mammals, they are indirect and slower to act. Here we investigated direct links between mammalian immune and coagulation systems by examining cytokine proproteins for potential thrombin protease consensus sites. We found that interleukin (IL)-1α is directly activated by thrombin. Thrombin cleaved pro-IL-1α at a site perfectly conserved across disparate species, indicating functional importance. Surface pro-IL-1α on macrophages and activated platelets was cleaved and activated by thrombin, while tissue factor, a potent thrombin activator, colocalized with pro-IL-1α in the epidermis. Mice bearing a mutation in the IL-1α thrombin cleavage site (R114Q) exhibited defects in efficient wound healing and rapid thrombopoiesis after acute platelet loss. Thrombin-cleaved IL-1α was detected in humans during sepsis, pointing to the relevance of this pathway for normal physiology and the pathogenesis of inflammatory and thrombotic diseases.
Excessive activation of the NLR family pyrin domain containing 3 (NLRP3) inflammasome is involved in many chronic inflammatory diseases, including cardiovascular and Alzheimer’s disease. Here we show that microtubule-affinity regulating kinase 4 (MARK4) binds to NLRP3 and drives it to the microtubule-organizing centre, enabling the formation of one large inflammasome speck complex within a single cell. MARK4 knockdown or knockout, or disruption of MARK4-NLRP3 interaction, impairs NLRP3 spatial arrangement and limits inflammasome activation. Our results demonstrate how an evolutionarily conserved protein involved in the regulation of microtubule dynamics orchestrates NLRP3 inflammasome activation by controlling its transport to optimal activation sites, and identify a targetable function for MARK4 in the control of innate immunity.
Splenic marginal zone B (MZB) cells, positioned at the interface between circulating blood and lymphoid tissue, detect and respond to blood-borne antigens. Here we show that MZB cells in mice activate a homeostatic program in response to a high-cholesterol diet (HCD) and regulate both the differentiation and accumulation of T follicular helper (T) cells. Feeding mice an HCD resulted in upregulated MZB cell surface expression of the immunoregulatory ligand PDL1 in an ATF3-dependent manner and increased the interaction between MZB cells and pre-T cells, leading to PDL1-mediated suppression of T cell motility, alteration of T cell differentiation, reduced T abundance and suppression of the proatherogenic T response. Our findings reveal a previously unsuspected role for MZB cells in controlling the T-germinal center response to a cholesterol-rich diet and uncover a PDL1-dependent mechanism through which MZB cells use their innate immune properties to limit an exaggerated adaptive immune response.
Type-2 innate lymphoid cells (ILC2) are a prominent source of type II cytokines and are found constitutively at mucosal surfaces and in visceral adipose tissue. Despite their role in limiting obesity, how ILC2s respond to high fat feeding is poorly understood, and their direct influence on the development of atherosclerosis has not been explored. Here, we show that ILC2 are present in para-aortic adipose tissue and lymph nodes and display an inflammatory-like phenotype atypical of adipose resident ILC2. High fat feeding alters both the number of ILC2 and their type II cytokine production. Selective genetic ablation of ILC2 in Ldlr−/− mice accelerates the development of atherosclerosis, which is prevented by reconstitution with wild type but not Il5−/− or Il13−/− ILC2. We conclude that ILC2 represent a major innate cell source of IL-5 and IL-13 required for mounting atheroprotective immunity, which can be altered by high fat diet.
IL‐1 is a powerful cytokine that drives inflammation and modulates adaptive immunity. Both IL‐1α and IL‐1β are translated as proforms that require cleavage for full cytokine activity and release, while IL‐1α is reported to occur as an alternative plasma membrane‐associated form on many cell types. However, the existence of cell surface IL‐1α (csIL‐1α) is contested, how IL‐1α tethers to the membrane is unknown, and signaling pathways controlling trafficking are not specified. Using a robust and fully validated system, we show that macrophages present bona fide csIL‐1α after ligation of TLRs. Pro‐IL‐1α tethers to the plasma membrane in part through IL‐1R2 or via association with a glycosylphosphatidylinositol‐anchored protein, and can be cleaved, activated, and released by proteases. csIL‐1α requires de novo protein synthesis and its trafficking to the plasma membrane is exquisitely sensitive to inhibition by IFN‐γ, independent of expression level. We also reveal how prior csIL‐1α detection could occur through inadvertent cell permeabilisation, and that senescent cells do not drive the senescent‐associated secretory phenotype via csIL‐1α, but rather via soluble IL‐1α. We believe these data are important for determining the local or systemic context in which IL‐1α can contribute to disease and/or physiological processes.
Background and aimExtensive studies have revealed an important protective function for IgM antibodies from B1a cells in atherosclerosis, whereas the role of B2 cells and IgG antibodies is uncertain, with both pro- and anti-atherogenic actions reported. The aim of this study was to specifically target antibodies but not other B cell functions and determine the effect on mouse atherosclerosis.MethodsWe created MB1-Cre x XBP1fl/fl mice that have B cell specific deficiency in the unfolded protein response transcription factor XBP1, previously reported to result in a specific antibody secretion defect. Specific antibody responses were assessed by ELISA and ELISpot after immunisation with NP-chicken gamma globulin. Chimeric Ldlr
-/– mice with bone marrow from MB1-Cre x XBP1fl/fl or control mice were fed a western diet for 8 weeks.ResultsB cell XBP1 deficiency led to significantly attenuated antibody secretion after NP-CGG immunisation. Analysis of ldlr–/– chimeric mice revealed enhanced atherosclerosis progression in MB1-Cre x XBP1fl/fl recipients. These mice displayed severely attenuated serum IgM, IgG and IgE levels, but intact spleen, lymph node and peritoneal B cells. There were no differences in total cholesterol levels. Antibody deficiency was associated with enhanced pro-atherogenic Th1 CD4+ T cell immunity.ConclusionsAntibodies have an overall protective effect on atherosclerosis and B2 cell antibodies are not responsible for enhanced atherosclerosis in IgM-deficient mice. Other B cell functions may be pathogenic in atherosclerosis.
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