TREM2 protects from atherosclerosis by limiting necrotic core formation.

Atherosclerosis is a chronic disease of the vascular wall driven by lipid accumulation and inflammation in the intimal layer of arteries, and its main complications, myocardial infarction and stroke, are the leading cause of mortality worldwide [1], [2]. Recent studies have identified Triggering receptor expressed on myeloid cells 2 (TREM2), a lipid-sensing receptor regulating myeloid cell functions [3], to be highly expressed in macrophage foam cells in experimental and human atherosclerosis [4]. However, the role of TREM2 in atherosclerosis is not fully known. Here, we show that hematopoietic or global TREM2 deficiency increased, whereas TREM2 agonism decreased necrotic core formation in early atherosclerosis. We demonstrate that TREM2 is essential for the efferocytosis capacities of macrophages, and to the survival of lipid-laden macrophages, indicating a crucial role of TREM2 in maintaining the balance between foam cell death and clearance of dead cells in atherosclerotic lesions, thereby controlling plaque necrosis.

Combined Effects of Clonal Hematopoiesis and Carotid Stenosis on Cardiovascular Mortality.

BACKGROUND: The expansion of hematopoietic stem cells caused by acquired somatic mutations (clonal hematopoiesis [CH]) is a novel cardiovascular risk factor. The prognostic value of CH in patients with carotid atherosclerosis remains to be evaluated. OBJECTIVES: This study assessed the prognostic significance of CH in patients with atherosclerosis as detected by ultrasound of the carotid artery. METHODS: We applied deep sequencing of selected genomic regions within the genes DNMT3A, TET2, ASXL1, and JAK2 to screen for CH in 968 prospectively collected patients with asymptomatic carotid atherosclerosis evaluated by duplex sonography. RESULTS: We detected clonal markers at variant allele frequency ≥2% in 133 (13.7%) of 968 patients (median age 69.2 years), with increasing prevalence at advanced age. Multivariate analyses including age and established cardiovascular risk factors revealed overall presence of CH to be significantly associated with increased risk of cardiovascular death (HR: 1.50; 95% CI: 1.12-2.00; P = 0.007), reflected also at the single gene level. The effect of CH was more pronounced in older patients and independent of the patients' inflammatory status as measured by high-sensitivity C-reactive protein. Simultaneous assessment of CH and degree of carotid stenosis revealed combined effects on cardiovascular mortality, depicted by a superior risk for patients with >50% stenosis and concomitant CH (adjusted HR: 1.60; 95% CI: 1.08-2.38; P = 0.020). CONCLUSIONS: CH status in combination with the extent of carotid atherosclerosis jointly predict long-term mortality. Determination of CH can provide additional prognostic information in patients with asymptomatic carotid atherosclerosis.

Loss of TET2 increases B-1 cell number and IgM production while limiting CDR3 diversity.

Recent studies have demonstrated a role for Ten-Eleven Translocation-2 (TET2), an epigenetic modulator, in regulating germinal center formation and plasma cell differentiation in B-2 cells, yet the role of TET2 in regulating B-1 cells is largely unknown. Here, B-1 cell subset numbers, IgM production, and gene expression were analyzed in mice with global knockout of TET2 compared to wildtype (WT) controls. Results revealed that TET2-KO mice had elevated numbers of B-1a and B-1b cells in their primary niche, the peritoneal cavity, as well as in the bone marrow (B-1a) and spleen (B-1b). Consistent with this finding, circulating IgM, but not IgG, was elevated in TET2-KO mice compared to WT. Analysis of bulk RNASeq of sort purified peritoneal B-1a and B-1b cells revealed reduced expression of heavy and light chain immunoglobulin genes, predominantly in B-1a cells from TET2-KO mice compared to WT controls. As expected, the expression of IgM transcripts was the most abundant isotype in B-1 cells. Yet, only in B-1a cells there was a significant increase in the proportion of IgM transcripts in TET2-KO mice compared to WT. Analysis of the CDR3 of the BCR revealed an increased abundance of replicated CDR3 sequences in B-1 cells from TET2-KO mice, which was more clearly pronounced in B-1a compared to B-1b cells. V-D-J usage and circos plot analysis of V-J combinations showed enhanced usage of VH11 and VH12 pairings. Taken together, our study is the first to demonstrate that global loss of TET2 increases B-1 cell number and IgM production and reduces CDR3 diversity, which could impact many biological processes and disease states that are regulated by IgM.

Effects of Tulp4 deficiency on murine embryonic development and adult phenotype.

Genetically engineered mouse models have the potential to unravel fundamental biological processes and provide mechanistic insights into the pathogenesis of human diseases. We have previously observed that germline genetic variation at the TULP4 locus influences clinical characteristics in patients with myeloproliferative neoplasms. To elucidate the role of TULP4 in pathological and physiological processes in vivo, we generated a Tulp4 knockout mouse model. Systemic Tulp4 deficiency exerted a strong impact on embryonic development in both Tulp4 homozygous null (Tulp4-/-) and heterozygous (Tulp4+/-) knockout mice, the former exhibiting perinatal lethality. High-resolution episcopic microscopy (HREM) of day 14.5 embryos allowed for the identification of multiple developmental defects in Tulp4-/- mice, including severe heart defects. Moreover, in Tulp4+/- embryos HREM revealed abnormalities of several organ systems, which per se do not affect prenatal or postnatal survival. In adult Tulp4+/- mice, extensive examinations of hematopoietic and cardiovascular features, involving histopathological surveys of multiple tissues as well as blood counts and immunophenotyping, did not provide evidence for anomalies as observed in corresponding embryos. Finally, evaluating a potential obesity-related phenotype as reported for other TULP family members revealed a trend for increased body weight of Tulp4+/- mice. RESEARCH HIGHLIGHTS: To study the role of the TULP4 gene in vivo, we generated a Tulp4 knockout mouse model. Correlative analyses involving HREM revealed a strong impact of Tulp4 deficiency on murine embryonic development.

Mutational landscape of intestinal crypt cells after long-term in vivo exposure to high fat diet.

Obesity is a modifiable risk factor in cancer development, especially for gastrointestinal cancer. While the etiology of colorectal cancer is well characterized by the adenoma-carcinoma sequence, it remains unclear how obesity influences colorectal cancer development. Dietary components of a high fat diet along with obesity have been shown to modulate the cancer risk by perturbing the homeostasis of intestinal stem cells, yet how adiposity impacts the development of genomic instability has not been studied. Mutational signatures are a powerful way to understand how a complex biological response impacts genomic stability. We utilized a mouse model of diet-induced obesity to study the mutational landscape of intestinal crypt cells after a 48-week exposure to an experimental high fat diet in vivo. By clonally enriching single crypt derived cells in organoid culture and obtaining whole genome sequences, we analyzed and compared the mutational landscape of intestinal epithelial cells from normal diet and high fat diet mice. Single nucleotide substitution signatures and indel signatures present in our cohort are found equally active in both diet groups and reflect biological processes of normal aging, cellular replication, and oxidative stress induced during organoid culturing. Thus, we demonstrate that in the absence of activating mutations or chemical exposure, high fat diet alone is not sufficient to increase genomic instability.

Cell-autonomous regulation of complement C3 by factor H limits macrophage efferocytosis and exacerbates atherosclerosis.

Complement factor H (CFH) negatively regulates consumption of complement component 3 (C3), thereby restricting complement activation. Genetic variants in CFH predispose to chronic inflammatory disease. Here, we examined the impact of CFH on atherosclerosis development. In a mouse model of atherosclerosis, CFH deficiency limited plaque necrosis in a C3-dependent manner. Deletion of CFH in monocyte-derived inflammatory macrophages propagated uncontrolled cell-autonomous C3 consumption without downstream C5 activation and heightened efferocytotic capacity. Among leukocytes, Cfh expression was restricted to monocytes and macrophages, increased during inflammation, and coincided with the accumulation of intracellular C3. Macrophage-derived CFH was sufficient to dampen resolution of inflammation, and hematopoietic deletion of CFH in atherosclerosis-prone mice promoted lesional efferocytosis and reduced plaque size. Furthermore, we identified monocyte-derived inflammatory macrophages expressing C3 and CFH in human atherosclerotic plaques. Our findings reveal a regulatory axis wherein CFH controls intracellular C3 levels of macrophages in a cell-autonomous manner, evidencing the importance of on-site complement regulation in the pathogenesis of inflammatory diseases.

C4b-binding protein inhibits particulate- and crystalline-induced NLRP3 inflammasome activation.

Dysregulated NLRP3 inflammasome activation drives a wide variety of diseases, while endogenous inhibition of this pathway is poorly characterised. The serum protein C4b-binding protein (C4BP) is a well-established inhibitor of complement with emerging functions as an endogenously expressed inhibitor of the NLRP3 inflammasome signalling pathway. Here, we identified that C4BP purified from human plasma is an inhibitor of crystalline- (monosodium urate, MSU) and particulate-induced (silica) NLRP3 inflammasome activation. Using a C4BP mutant panel, we identified that C4BP bound these particles via specific protein domains located on the C4BP α-chain. Plasma-purified C4BP was internalised into MSU- or silica-stimulated human primary macrophages, and inhibited MSU- or silica-induced inflammasome complex assembly and IL-1ß cytokine secretion. While internalised C4BP in MSU or silica-stimulated human macrophages was in close proximity to the inflammasome adaptor protein ASC, C4BP had no direct effect on ASC polymerisation in in vitro assays. C4BP was also protective against MSU- and silica-induced lysosomal membrane damage. We further provide evidence for an anti-inflammatory function for C4BP in vivo, as C4bp-/- mice showed an elevated pro-inflammatory state following intraperitoneal delivery of MSU. Therefore, internalised C4BP is an inhibitor of crystal- or particle-induced inflammasome responses in human primary macrophages, while murine C4BP protects against an enhanced inflammatory state in vivo. Our data suggests C4BP has important functions in retaining tissue homeostasis in both human and mice as an endogenous serum inhibitor of particulate-stimulated inflammasome activation.

Familial hypercholesterolemia: A systematic review of modeling studies on screening interventions.

BACKGROUND AND AIMS: FH is still underdiagnosed. Cost-effectiveness results of preventive screening strategies vary. We aimed at systematically assessing the benefits, harms and cost effectiveness of screening for familial hypercholesterolemia (FH) and at providing an overview of the main characteristics and methodological approaches of applied decision-analytic models. METHODS: A systematic literature search was conducted in MEDLINE, EconLit, CRD-databases and the CEA-registry for FH screening starting 2012. Earlier studies were included from a published systematic review. Results were reported in standardized semi-quantitative evidence tables. Costs were converted to current euros. Incremental cost-effectiveness ratios (ICERs) were recalculated according to economic guidelines. RESULTS: Out of our 211 retrieved studies, eight were included in the review in addition to six studies from an earlier review. Studies were conducted in Europe (UK, The Netherlands, Spain, Poland), USA and Australia evaluating cascade (CS), opportunistic (OS), universal screening (UniS), or combinations using genetic testing, clinical criteria or combinations. Studies evaluating only CS identified strategies with an ICER of up to 37,100 EUR/quality-adjusted life-year (QALY) but some strategies were dominated depending on test combinations. UniS of newborns in combination with CS had an ICER≤15,000 EUR/QALY for sequential cholesterol-genetic screening. In other studies, UniS was dominated by OS/CS. CONCLUSIONS: Our systematic review demonstrates the values of FH screening and provides an overview of potentially relevant screening strategies to be tested using a decision-analytic model for the respective country or region. Future research is needed on the transferability of results to other countries and modeling spillover effects to newborns.

Soluble TREM2 levels reflect the recruitment and expansion of TREM2+ macrophages that localize to fibrotic areas and limit NASH.

BACKGROUND & AIMS: Previous single-cell RNA-sequencing analyses have shown that Trem2-expressing macrophages are present in the liver during obesity, non-alcoholic steatohepatitis (NASH) and cirrhosis. Herein, we aimed to functionally characterize the role of bone marrow-derived TREM2-expressing macrophage populations in NASH. METHODS: We used bulk RNA sequencing to assess the hepatic molecular response to lipid-dependent dietary intervention in mice. Spatial mapping, bone marrow transplantation in two complementary murine models and single-cell sequencing were applied to functionally characterize the role of TREM2+ macrophage populations in NASH. RESULTS: We found that the hepatic transcriptomic profile during steatohepatitis mirrors the dynamics of recruited bone marrow-derived monocytes that already acquire increased expression of Trem2 in the circulation. Increased Trem2 expression was reflected by elevated levels of systemic soluble TREM2 in mice and humans with NASH. In addition, soluble TREM2 levels were superior to traditionally used laboratory parameters for distinguishing between different fatty liver disease stages in two separate clinical cohorts. Spatial transcriptomics revealed that TREM2+ macrophages localize to sites of hepatocellular damage, inflammation and fibrosis in the steatotic liver. Finally, using multiple murine models and in vitro experiments, we demonstrate that hematopoietic Trem2 deficiency causes defective lipid handling and extracellular matrix remodeling, resulting in exacerbated steatohepatitis, cell death and fibrosis. CONCLUSIONS: Our study highlights the functional properties of bone marrow-derived TREM2+ macrophages and implies the clinical relevance of systemic soluble TREM2 levels in the context of NASH. LAY SUMMARY: Our study defines the origin and function of macrophages (a type of immune cell) that are present in the liver and express a specific protein called TREM2. We find that these cells have an important role in protecting against non-alcoholic steatohepatitis (a progressive form of fatty liver disease). We also show that the levels of soluble TREM2 in the blood could serve as a circulating marker of non-alcoholic fatty liver disease.

Tim-1 mucin domain-mutant mice display exacerbated atherosclerosis.

BACKGROUND AND AIMS: Increasing evidence has shown that immune checkpoint molecules of the T-cell immunoglobulin and mucin domain (Tim) family are associated with diverse physiologic and pathologic processes. Previous studies of the role of Tim-1 in atherosclerosis using anti-Tim-1 antibodies have yielded contradictory results. We thus aimed to investigate atherosclerosis development in Tim-1 deficient mice. METHODS: Mice with a specific loss of the Tim-1 mucin-domain (Tim-1Δmucin) and C57BL/6 (WT) mice received a single injection of a recombinant adeno-associated virus encoding murine Pcsk9 (rAAV2/8-D377Y-mPcsk9) and were fed a Western type diet for 13 weeks to introduce atherosclerosis. RESULTS: Tim-1Δmucin mice developed significantly larger lesions in the aortic root compared to WT mice, with significantly more macrophages and a trend towards a larger necrotic core. Furthermore, Tim-1Δmucin mice showed a significant loss of IL-10+ B cells and regulatory B cell subsets and increased pro-atherogenic splenic follicular B cells compared to WT mice. Moreover, Tim-1Δmucin mice displayed a dramatic reduction in Th2-associated immune response compared to controls but we did not observe any changes in humoral immunity. CONCLUSIONS: In summary, Tim-1Δmucin mice displayed a profound impairment in IL-10+ B cells and an imbalance in the Th1/Th2 ratio, which associated with exacerbated atherosclerosis.

Mitochondrial C5aR1 activity in macrophages controls IL-1ß production underlying sterile inflammation.

While serum-circulating complement destroys invading pathogens, intracellularly active complement, termed the "complosome," functions as a vital orchestrator of cell-metabolic events underlying T cell effector responses. Whether intracellular complement is also nonredundant for the activity of myeloid immune cells is currently unknown. Here, we show that monocytes and macrophages constitutively express complement component (C) 5 and generate autocrine C5a via formation of an intracellular C5 convertase. Cholesterol crystal sensing by macrophages induced C5aR1 signaling on mitochondrial membranes, which shifted ATP production via reverse electron chain flux toward reactive oxygen species generation and anaerobic glycolysis to favor IL-1ß production, both at the transcriptional level and processing of pro­IL-1ß. Consequently, atherosclerosis-prone mice lacking macrophage-specific C5ar1 had ameliorated cardiovascular disease on a high-cholesterol diet. Conversely, inflammatory gene signatures and IL-1ß produced by cells in unstable atherosclerotic plaques of patients were normalized by a specific cell-permeable C5aR1 antagonist. Deficiency of the macrophage cell-autonomous C5 system also protected mice from crystal nephropathy mediated by folic acid. These data demonstrate the unexpected intracellular formation of a C5 convertase and identify C5aR1 as a direct modulator of mitochondrial function and inflammatory output from myeloid cells. Together, these findings suggest that the complosome is a contributor to the biologic processes underlying sterile inflammation and indicate that targeting this system could be beneficial in macrophage-dependent diseases, such as atherosclerosis.

Impact of Specific N-Glycan Modifications on the Use of Plant-Produced SARS-CoV-2 Antigens in Serological Assays.

The receptor binding domain (RBD) of the SARS-CoV-2 spike protein plays a key role in the virus-host cell interaction, and viral infection. The RBD is a major target for neutralizing antibodies, whilst recombinant RBD is commonly used as an antigen in serological assays. Such assays are essential tools to gain control over the pandemic and detect the extent and durability of an immune response in infected or vaccinated populations. Transient expression in plants can contribute to the fast production of viral antigens, which are required by industry in high amounts. Whilst plant-produced RBDs are glycosylated, N-glycan modifications in plants differ from humans. This can give rise to the formation of carbohydrate epitopes that can be recognized by anti-carbohydrate antibodies present in human sera. For the performance of serological tests using plant-produced recombinant viral antigens, such cross-reactive carbohydrate determinants (CCDs) could result in false positives. Here, we transiently expressed an RBD variant in wild-type and glycoengineered Nicotiana benthamiana leaves and characterized the impact of different plant-specific N-glycans on RBD reactivity in serological assays. While the overall performance of the different RBD glycoforms was comparable to each other and to a human cell line produced RBD, there was a higher tendency toward false positive results with sera containing allergy-related CCD-antibodies when an RBD carrying ß1,2-xylose and core α1,3-fucose was used. These rare events could be further minimized by pre-incubating sera from allergic individuals with a CCD-inhibitor. Thereby, false positive signals obtained from anti-CCD antibodies, could be reduced by 90%, on average.

APRIL limits atherosclerosis by binding to heparan sulfate proteoglycans.

Atherosclerotic cardiovascular disease causes heart attacks and strokes, which are the leading causes of mortality worldwide1. The formation of atherosclerotic plaques is initiated when low-density lipoproteins bind to heparan-sulfate proteoglycans (HSPGs)2 and become trapped in the subendothelial space of large and medium size arteries, which leads to chronic inflammation and remodelling of the artery wall2. A proliferation-inducing ligand (APRIL) is a cytokine that binds to HSPGs3, but the physiology of this interaction is largely unknown. Here we show that genetic ablation or antibody-mediated depletion of APRIL aggravates atherosclerosis in mice. Mechanistically, we demonstrate that APRIL confers atheroprotection by binding to heparan sulfate chains of heparan-sulfate proteoglycan 2 (HSPG2), which limits the retention of low-density lipoproteins, accumulation of macrophages and formation of necrotic cores. Indeed, antibody-mediated depletion of APRIL in mice expressing heparan sulfate-deficient HSPG2 had no effect on the development of atherosclerosis. Treatment with a specific anti-APRIL antibody that promotes the binding of APRIL to HSPGs reduced experimental atherosclerosis. Furthermore, the serum levels of a form of human APRIL protein that binds to HSPGs, which we termed non-canonical APRIL (nc-APRIL), are associated independently of traditional risk factors with long-term cardiovascular mortality in patients with atherosclerosis. Our data reveal properties of APRIL that have broad pathophysiological implications for vascular homeostasis.

Humoral immunity in atherosclerosis and myocardial infarction: from B cells to antibodies.

Immune mechanisms are critically involved in the pathogenesis of atherosclerosis and its clinical manifestations. Associations of specific antibody levels and defined B-cell subsets with cardiovascular disease activity in humans as well as mounting evidence from preclinical models demonstrate a role of B cells and humoral immunity in atherosclerotic cardiovascular disease. These include all aspects of B-cell immunity, the generation of antigen-specific antibodies, antigen presentation and co-stimulation of T cells, as well as production of cytokines. Through their impact on adaptive and innate immune responses and the regulation of many other immune cells, B cells mediate both protective and detrimental effects in cardiovascular disease. Several antigens derived from (oxidized) lipoproteins, the vascular wall and classical autoantigens have been identified. The unique antibody responses they trigger and their relationship with atherosclerotic cardiovascular disease are reviewed. In particular, we focus on the different effector functions of specific IgM, IgG, and IgE antibodies and the cellular responses they trigger and highlight potential strategies to target B-cell functions for therapy.

Pharmacological inhibition of fatty acid oxidation reduces atherosclerosis progression by suppression of macrophage NLRP3 inflammasome activation.

BACKGROUND: Inflammation is a key process during atherosclerotic lesion development and propagation. Recent evidence showed clearly that especially the inhibition of interleukin (IL)-1ß reduced atherosclerotic adverse events in human patients. Fatty acid oxidation (FAO) was previously demonstrated to interact with the NOD-, LRR- and pyrin domain-containing protein 3 (NLRP3) pathway which is required for mature IL-1ß secretion. To understand possible anti-inflammatory properties of FAO inhibition, we tested the effect of pharmacological FAO inhibition using the inhibitor for long-chain 3-ketoacyl coenzyme A thiolase trimetazidine on atherosclerotic plaque development and inflammation. EXPERIMENTAL APPROACH: The effect of FAO inhibition was determined in LDL-R-/- male mice on a C57/BL6 background. In vitro effects of trimetazidine treatment were analyzed in human umbilical vein endothelial cells and human monocyte derived macrophages. KEY RESULTS: We were able to demonstrate that inhibition of FAO reduced atherosclerotic plaque growth. We did not find direct anti-inflammatory properties of trimetazidine in endothelial cells or macrophages in vitro. However, we found that the activation of the NLRP3 system and the secretion of IL-1ß were significantly reduced in macrophages after FAO inhibition. These results were confirmed in atherosclerotic lesions of mice treated with trimetazidine as they showed a significant reduction of IL-1ß and cleaved caspase-1 in the atherosclerotic lesion as well as of IL-1ß and IL-18 in the circulation. CONCLUSION: Overall, we therefore suggest that the main mechanism of reducing inflammation of trimetazidine and FAO inhibition is the reduction of the NLRP-3 activation leading to reduced levels of the proinflammatory cytokine IL-1ß.

Hematopoietic expression of a chimeric murine-human CALR oncoprotein allows the assessment of anti-CALR antibody immunotherapies in vivo.

Myeloproliferative neoplasms (MPNs) are characterized by a pathologic expansion of myeloid lineages. Mutations in JAK2, CALR and MPL genes are known to be three prominent MPN disease drivers. Mutant CALR (mutCALR) is an oncoprotein that interacts with and activates the thrombopoietin receptor (MPL) and represents an attractive target for targeted therapy of CALR mutated MPN. We generated a transgenic murine model with conditional expression of the human mutant exon 9 (del52) from the murine endogenous Calr locus. These mice develop essential thrombocythemia like phenotype with marked thrombocytosis and megakaryocytosis. The disease exacerbates with age showing prominent signs of splenomegaly and anemia. The disease is transplantable and mutCALR stem cells show proliferative advantage when compared to wild type stem cells. Transcriptome profiling of hematopoietic stem cells revealed oncogenic and inflammatory gene expression signatures. To demonstrate the applicability of the transgenic animals for immunotherapy, we treated mice with monoclonal antibody raised against the human mutCALR. The antibody treatment lowered platelet and stem cell counts in mutant mice. Secretion of mutCALR did not constitute a significant antibody sink. This animal model not only recapitulates human MPN but also serves as a relevant model for testing immunotherapeutic strategies targeting epitopes of the human mutCALR.

SERUM LEVELS OF ANTIBODIES AGAINST OXIDATION-SPECIFIC EPITOPES ARE DECREASED IN PATIENTS WITH RETINAL VEIN OCCLUSION.

PURPOSE: Oxidative stress and inflammation have been implicated in the development of retinal vein occlusion (RVO). Oxidation-specific epitopes (OSEs) represent products of oxidative stress that can trigger vascular inflammation and thrombosis. Natural occurring antibodies have been shown to bind oxidation-specific epitopes thereby inhibiting their inflammatory potential and promoting their removal. METHODS: This prospective cross-sectional study included 270 patients with RVO and 81 in-hospital control patients. We measured three types of serum levels of oxidation-specific epitope-specific immunoglobulin M and immunoglobulin G antibodies (anti-copper-oxidized LDL [CuOx-LDL], antiphosphocholine [PC], anti-malondialdehyde-modified LDL [MDA-LDL]). History of arterial hypertension, hyperlipidemia, myocardial infarction, diabetes mellitus, stroke, smoking status, and several laboratory parameters were determined to control for potential confounders. RESULTS: Compared with controls, patients with RVO had significantly lower levels of immunoglobulin M and immunoglobulin G antibodies against CuOx-LDL and PC, and significantly lower levels of immunoglobulin G but not immunoglobulin M antibodies against MDA-LDL. The association between RVO patients and lower levels of these antibodies prevailed upon multivariable adjustment. CONCLUSION: These prospective data show that antibodies against oxidation-specific epitope are lower in patients with RVO compared with control patients and support the concept that oxidative stress and inflammation play key roles in the development and subsequent complications in RVO.

Oxidation-Specific Epitopes in Non-Alcoholic Fatty Liver Disease.

An improper balance between the production and elimination of intracellular reactive oxygen species causes increased oxidative stress. Consequently, DNA, RNA, proteins, and lipids are irreversibly damaged, leading to molecular modifications that disrupt normal function. In particular, the peroxidation of lipids in membranes or lipoproteins alters lipid function and promotes formation of neo-epitopes, such as oxidation-specific epitopes (OSEs), which are found to be present on (lipo)proteins, dying cells, and extracellular vesicles. Accumulation of OSEs and recognition of OSEs by designated pattern recognition receptors on immune cells or soluble effectors can contribute to the development of chronic inflammatory diseases. In line, recent studies highlight the involvement of modified lipids and OSEs in different stages of the spectrum of non-alcoholic fatty liver disease (NAFLD), including inflammatory non-alcoholic steatohepatitis (NASH), fibrosis, and hepatocellular carcinoma. Targeting lipid peroxidation products shows high potential in the search for novel, better therapeutic strategies for NASH.

SIRPα on Mouse B1 Cells Restricts Lymphoid Tissue Migration and Natural Antibody Production.

The inhibitory immunoreceptor SIRPα is expressed on myeloid and neuronal cells and interacts with the broadly expressed CD47. CD47-SIRPα interactions form an innate immune checkpoint and its targeting has shown promising results in cancer patients. Here, we report expression of SIRPα on B1 lymphocytes, a subpopulation of murine B cells responsible for the production of natural antibodies. Mice defective in SIRPα signaling (SIRPαΔCYT mice) displayed an enhanced CD11b/CD18 integrin-dependent B1 cell migration from the peritoneal cavity to the spleen, local B1 cell accumulation, and enhanced circulating natural antibody levels, which was further amplified upon immunization with T-independent type 2 antigen. As natural antibodies are atheroprotective, we investigated the involvement of SIRPα signaling in atherosclerosis development. Bone marrow (SIRPαΔCYT>LDLR-/-) chimaeric mice developed reduced atherosclerosis accompanied by increased natural antibody production. Collectively, our data identify SIRPα as a unique B1 cell inhibitory receptor acting to control B1 cell migration, and imply SIRPα as a potential therapeutic target in atherosclerosis.

The cytoskeletal regulator HEM1 governs B cell development and prevents autoimmunity.

The WAVE regulatory complex (WRC) is crucial for assembly of the peripheral branched actin network constituting one of the main drivers of eukaryotic cell migration. Here, we uncover an essential role of the hematopoietic-specific WRC component HEM1 for immune cell development. Germline-encoded HEM1 deficiency underlies an inborn error of immunity with systemic autoimmunity, at cellular level marked by WRC destabilization, reduced filamentous actin, and failure to assemble lamellipodia. Hem1-/- mice display systemic autoimmunity, phenocopying the human disease. In the absence of Hem1, B cells become deprived of extracellular stimuli necessary to maintain the strength of B cell receptor signaling at a level permissive for survival of non-autoreactive B cells. This shifts the balance of B cell fate choices toward autoreactive B cells and thus autoimmunity.