Abstract.  Pagano S, Satta N, Werling D, Offord V, de Moerloose P, Charbonney E, Hochstrasser D, Roux‐Lombard P, Vuilleumier N (Geneva University Hospital and Faculty of Medicine, Geneva, Switzerland; Geneva University Hospital and Faculty of Medicine, Geneva, Switzerland; Royal Veterinary College, Hertfordshire, UK; St. Michael’s Hospital, Toronto, Canada; Geneva University Hospital and Faculty of Medicine, Geneva, Switzerland). Anti‐apolipoprotein A‐1 IgG in patients with myocardial infarction promotes inflammation through TLR2/CD14 complex. J Intern Med 2012; 272: 344–357.Objectives.  Toll‐like receptor (TLR)‐mediated vascular inflammation, inducible by – amongst other factors – auto‐antibodies, is increasingly recognized as a potential mediator of cardiovascular disease. We investigated whether anti‐apolipoprotein (Apo)A‐1 IgG was associated with a pro‐inflammatory cytokine profile in myocardial infarction (MI) patients and whether anti‐ApoA‐1 IgG elicited a pro‐inflammatory response by activating TLRs.Methods.  As surrogate markers of atherosclerotic plaque vulnerability, interleukin (IL)‐6, tumour necrosis factor (TNF)‐α, matrix metalloproteinase (MMP)‐9 and MMP‐3 levels were assessed in 221 consecutive MI patients. Using human monocyte‐derived macrophages (HMDMs) we investigated (i) the anti‐ApoA‐1 IgG interaction with TLRs using proximity ligation assay and (ii) anti‐ApoA‐1 IgG‐dependent IL‐6/TNF‐α production. TLR involvement was further confirmed using HEK293‐Blue TLR‐2/‐4 cells and by computational docking simulations.Results.  In MI patients, anti‐ApoA‐1 IgG positivity was associated with higher levels of IL‐6, TNF‐α and MMP‐9, but lower MMP‐3 levels. In in vitro experiments, anti‐ApoA‐1 antibodies bound to HDMDs in a TLR2‐dependent manner, resulting in nuclear translocation of NFκB and a significant increase in TNF‐α and IL‐6 production. Subsequent functional studies highlighted the importance of CD14 as co‐receptor in the anti‐ApoA‐1 IgG–TLR2‐induced cytokine production. Additional bioinformatic studies identified structural homologies between TLR2 and ApoA‐1, which may explain the observed cross‐reactivity between antibodies against these two molecules.Conclusions.  Anti‐ApoA‐1 IgG positivity in MI is associated with a high‐risk cytokine profile. These auto‐antibodies promote inflammation by stimulating the TLR2/CD14 receptor complex, probably because of molecular mimicry, which may contribute to atherosclerosis‐related complications in patients.

Background: SARS‐CoV‐2 infection triggers different auto‐antibodies, including anti‐apolipoprotein A‐1 IgGs (AAA1), which could be of concern as mediators of persistent symptoms. We determined the kinetics of AAA1 response over after COVID‐19 and the impact of AAA1 on the inflammatory response and symptoms persistence.Methods: All serologies were assessed at one, three, six and twelve months in 193 hospital employees with COVID‐19. ROC curve analyses and logistic regression models (LRM) were used to determine the prognostic accuracy of AAA1 and their association with patient‐reported COVID‐19 symptoms persistence at 12 months. Interferon (IFN)‐α and‐γ production by AAA1‐stimulated human monocyte‐derived macrophages (HMDM) was assessed in vitro.Results: AAA1 seropositivity was 93% at one month and declined to 15% at 12 months after COVID‐19. Persistent symptoms at 12 months were observed in 45.1% of participants, with a predominance of neurological (28.5%), followed by general (15%) and respiratory symptoms (9.3%). Over time, strength of correlations between AAA1 and anti‐SARS‐COV2 serologies decreased, but remained significant. From the 3^rd month on, AAA1 levels predicted persistent respiratory symptoms (area under the curves 0.72‐0.74; p < 0.001), independently of disease severity, age and gender (adjusted odds ratios 4.81–4.94; p = 0.02), while anti‐SARS‐CoV‐2 serologies did not. AAA1 increased IFN‐α production by HMDMs (p = 0.03), without affecting the IFN‐γ response.Conclusion: COVID‐19 induces a marked though transient AAA1 response, independently predicting one‐year persistence of respiratory symptoms. By increasing IFN‐α response, AAA1 may contribute to persistent symptoms. If and how AAA1 levels assessment could be of use for COVID‐19 risk stratification remains to be determined.

Humoral autoimmune-mediated inflammation plays a role in atherogenesis, and potentially in arterial thrombosis. Anti-apolipoprotein A-1 (apoA-1) IgG have been reported to represent emergent mediators of atherogenesis through Toll-like receptors (TLR) 2, 4 and CD14 signalling. We investigated the role of anti-apoA-1 IgG on tissue factor (TF) expression and activation, a key coagulation regulator underlying atherothrombosis. Atherothrombosis features were determined by immunohistochemical TF staining of human carotid biopsies derived from patients with severe carotid stenosis undergoing elective surgery (n=176), and on aortic roots of different genetic backgrounds mice (ApoE^-/-; TLR2^-/-ApoE^-/- and TLR4^-/-ApoE^-/-) exposed to passive immunisation with anti-apoA-1 IgG. Human serum levels of anti-apoA-1 IgG were measured by ELISA. In vitro, on human-monocyte-derived-macrophages (HMDM) the anti-apoA-1 IgG increased TF expression and activity were analysed by FACS and chromogenic assays in presence of different pharmacological inhibitors. Human serum anti-apoA-1 IgG levels significantly correlated to intraplaque TF expression in carotid biopsies (r=0.31, p<0.001), which was predictive of clinically symptomatic lesions. On HMDM, anti-apoA-1 IgG induced a TLR2, 4 and CD14-dependent increase in TF expression and activity, involving NF-kappaB and a c-Jun N-terminal kinase-dependent AP-1 transcription factors. In ApoE^-/- mice, anti-apoA-1 IgG passive immunisation significantly enhanced intraplaque TF expression when compared to control IgG. This effect was lost in both TLR2^-/-ApoE^-/- and TLR4^-/-ApoE^-/- mice. These results demonstrate that anti-apoA-1 IgG are associated with TF expression in human atherosclerotic plaques, induce TF expression in vitro and in vivo through TLR2 and 4 signalling, supporting a possible causal relationship between anti-apoA-1 IgG and atherothrombosis.

Dissecting the pathways regulating the adaptive immune response in atherosclerosis is of particular therapeutic interest. Here we report that the lipid G-protein-coupled receptor GPR55 is highly expressed by splenic plasma cells (PCs), upregulated in mouse spleens during atherogenesis and human unstable or ruptured compared to stable plaques.Gpr55-deficient mice developed larger atherosclerotic plaques with increased necrotic core size compared to their corresponding controls. Lack of GPR55 hyperactivated B cells, disturbed PC maturation and resulted in IgG overproduction. B-cell-specificGpr55depletion or adoptive transfer ofGpr55-deficient B cells was sufficient to promote plaque development and elevated IgG titers. In vitro, the endogenous GPR55 ligand lysophsophatidylinositol (LPI) enhanced PC proliferation, whereas GPR55 antagonism blocked PC maturation and increased their mitochondrial content. Collectively, these discoveries provide previously undefined evidence for GPR55 in B cells as a key modulator of the adaptive immune response in atherosclerosis.

A novel severe acute respiratory syndrome coronavirus (SARS-CoV-2) is the source of a current pandemic (COVID-19) with devastating consequences in public health and economic stability. Using a peptide array to map the antibody response of plasma from healing patients, we identified immunodominant linear epitopes corresponding to key proteolytic sites on the spike protein.

Aims: Anti-Apolipoprotein A-1 autoantibodies (anti-ApoA-1 IgG) promote atherogenesis via innate immune receptors, and may impair cellular cholesterol homeostasis (CH). We explored the presence of anti-ApoA-1 IgG in children (5–15 years old) with or without familial hypercholesterolemia (FH), analyzing their association with lipid profiles, and studied their in vitro effects on foam cell formation, gene regulation, and their functional impact on cholesterol passive diffusion (PD). Methods: Anti-ApoA-1 IgG and lipid profiles were measured on 29 FH and 25 healthy children. The impact of anti-ApoA-1 IgG on key CH regulators (SREBP2, HMGCR, LDL-R, ABCA1, and miR-33a) and foam cell formation detected by Oil Red O staining were assessed using human monocyte-derived macrophages. PD experiments were performed using a validated THP-1 macrophage model. Results: Prevalence of high anti-ApoA-1 IgG levels (seropositivity) was about 38% in both study groups. FH children seropositive for anti-ApoA-1 IgG had significant lower total cholesterol LDL and miR-33a levels than those who were seronegative. On macrophages, anti-ApoA-1 IgG induced foam cell formation in a toll-like receptor (TLR) 2/4-dependent manner, accompanied by NF-kB- and AP1-dependent increases of SREBP-2, LDL-R, and HMGCR. Despite increased ABCA1 and decreased mature miR-33a expression, the increased ACAT activity decreased membrane free cholesterol, functionally culminating to PD inhibition. Conclusions: Anti-ApoA-1 IgG seropositivity is frequent in children, unrelated to FH, and paradoxically associated with a favorable lipid profile. In vitro, anti-ApoA-1 IgG induced foam cell formation through a complex interplay between innate immune receptors and key cholesterol homeostasis regulators, functionally impairing the PD cholesterol efflux capacity of macrophages.