Graphical Abstract Highlights d Chronic viral infection causes long-term transcriptome and proteome changes in the liver d Hepatocyte-intrinsic type I interferon (IFN-I) signaling regulates hepatic metabolism d IFN-I signaling reprograms the urea cycle in hepatocytes and alters serum metabolites d Serum levels of arginine and ornithine modulate T cell responses and pathology

SummaryAtherosclerosis is initiated and sustained by hypercholesterolemia, which results in the generation of oxidized LDL (OxLDL) and other metabolic byproducts that trigger inflammation. Specific immune responses have been shown to modulate the inflammatory response during atherogenesis. The sialic acid-binding immunoglobulin-like lectin G (Siglec-G) is a negative regulator of the functions of several immune cells, including myeloid cells and B-1 cells. Here, we show that deficiency of Siglec-G in atherosclerosis-prone mice inhibits plaque formation and diet-induced hepatic inflammation. We further demonstrate that selective deficiency of Siglec-G in B cells alone is sufficient to mediate these effects. Levels of B-1 cell-derived natural IgM with specificity for OxLDL were significantly increased in the plasma and peritoneal cavity of Siglec-G-deficient mice. Consistent with the neutralizing functions of OxLDL-specific IgM, Siglec-G-deficient mice were protected from OxLDL-induced sterile inflammation. Thus, Siglec-G promotes atherosclerosis and hepatic inflammation by suppressing protective anti-inflammatory effector functions of B cells.

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Rationale: Deficiency of secreted IgM ( sIgM −/− ) accelerates atherosclerosis in Ldlr −/− mice. Several atheroprotective effects of increased levels of IgM antibodies have been suggested, including preventing inflammation induced by oxidized low-density lipoprotein and promoting apoptotic cell clearance. However, the mechanisms by which the lack of sIgM promotes lesion formation remain unknown. Objective: To identify the mechanisms by which sIgM deficiency accelerates atherosclerosis in mice. Methods and Results: We here show that both sIgM −/− and Ldlr −/− sIgM −/− mice develop increased plasma IgE titers because of impaired generation of B cells expressing the low-affinity IgE receptor CD23, which mediates the clearance of IgE antibodies. We further report that Ldlr −/− sIgM −/− mice exhibit increased numbers of activated mast cells and neutrophils in the perivascular area of atherosclerotic plaques. Treatment with an anti-IgE–neutralizing antibody fully reversed vascular inflammation and accelerated atherosclerotic lesion formation in cholesterol-fed Ldlr −/− sIgM −/− mice. Conclusions: Thus, our data identify a previously unsuspected mechanism by which sIgM deficiency aggravates atherosclerosis.

Atherosclerotic cardiovascular disease (CVD) is the leading cause of mortality worldwide 1,2 . Atherosclerotic plaque formation is initiated upon trapping of low-density lipoprotein (LDL) in the subendothelial space of large and medium size arteries that initially involves binding of LDL to heparan-sulfate proteoglycans (HSPGs) 3 , followed by a chronic inflammation and remodelling of the artery wall 3 . A Proliferation Inducing Ligand (APRIL), a cytokine produced by many cell types, binds to HSPGs 4 , 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 via binding to heparan sulfate (HS) chains of heparan-sulfate proteoglycan 2 (HSPG2), which limits LDL retention, macrophage accumulation and necrotic core formation. Indeed, antibody-mediated depletion of APRIL in mice expressing HS-deficient HSPG2 had no effect on atherosclerosis development.Consistent with these data, treatment with a specific anti-APRIL antibody that promotes the binding of APRIL to HSPGs reduces experimental atherosclerosis. Furthermore, the serum levels of a previously unknown 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 (10-to 12-year follow up) cardiovascular mortality in patients with atherosclerosis. Our data reveal hitherto unknown properties of APRIL that have broad pathophysiological implications for vascular homeostasis.

Genetic variants within complement factor H (CFH), a major alternative complement pathway regulator, are associated with the development of age-related macular degeneration (AMD) and other complementopathies. This is explained with the reduced binding of CFH or its splice variant factor H-like protein 1 (FHL-1) to self-ligands or altered self-ligands (e.g., malondialdehyde [MDA]-modified molecules) involved in homeostasis, thereby causing impaired complement regulation. Considering the critical role of CFH in inhibiting alternative pathway activation on MDA-modified surfaces, we performed an unbiased genome-wide search for genetic variants that modify the ability of plasma CFH to bind MDA in 1,830 individuals and characterized the mechanistic basis and the functional consequences of this. In a cohort of healthy individuals, we identified rs1061170 in CFH and the deletion of CFHR3 and CFHR1 as dominant genetic variants that modify CFH/FHL-1 binding to MDA. We further demonstrated that FHR1 and FHR3 compete with CFH for binding to MDA-epitopes and that FHR1 displays the highest affinity toward MDA-epitopes compared to CFH and FHR3. Moreover, FHR1 bound to MDA-rich areas on necrotic cells and prevented CFH from mediating its cofactor activity on MDA-modified surfaces, resulting in enhanced complement activation. These findings provide a mechanistic explanation as to why the deletion of CFHR3 and CFHR1 is protective in AMD and highlight the importance of genetic variants within the CFH/CFHR3/CFHR1 locus in the recognition of altered-self in tissue homeostasis.

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IRF8 expression in DCs plays a nonredundant role in the development of proatherogenic adaptive immunity.