Cross-species single-cell RNA sequencing reveals divergent phenotypes and activation states of adaptive immunity in human carotid and experimental murine atherosclerosis.

BACKGROUND AND AIMS: The distinct functions of immune cells in atherosclerosis have been mostly defined by preclinical mouse studies. Contrastingly, the immune cell composition of human atherosclerotic plaques and their contribution to disease progression is only poorly understood. It remains uncertain whether genetic animal models allow for valuable translational approaches. METHODS AND RESULTS: Single cell RNA-sequencing (scRNA-seq) was performed to define the immune cell landscape in human carotid atherosclerotic plaques. The human immune cell repertoire demonstrated an unexpectedly high heterogeneity and was dominated by cells of the T-cell lineage, a finding confirmed by immunohistochemistry. Bioinformatical integration with 7 mouse scRNA-seq data sets from adventitial and atherosclerotic vascular tissue revealed a total of 51 identities of cell types and differentiation states, of which some were only poorly conserved between species and exclusively found in humans. Locations, frequencies, and transcriptional programs of immune cells in mouse models did not resemble the immune cell landscape in human carotid atherosclerosis. In contrast to standard mouse models of atherosclerosis, human plaque leukocytes were dominated by several T-cell phenotypes with transcriptional hallmarks of T-cell activation and memory formation, T-cell receptor-, and pro-inflammatory signaling. Only mice at the age of 22 months partially resembled the activated T-cell phenotype. In a validation cohort of 43 patients undergoing carotid endarterectomy, the abundance of activated immune cell subsets in the plaque defined by multi-color flow cytometry associated with the extend of clinical atherosclerosis. CONCLUSIONS: Integrative scRNA-seq reveals a substantial difference in the immune cell composition of murine and human carotid atherosclerosis - a finding that questions the translational value of standard mouse models for adaptive immune cell studies. Clinical associations suggest a specific role for T-cell driven (auto-) immunity in human plaque formation and -instability.

A Meta-Analysis of Cumulative Incidence of Hepatocellular Carcinoma After the Fontan Operation.

BACKGROUND: Hepatic complications are increasingly recognized after the Fontan operation. The development of hepatocellular carcinoma (HCC) is associated with high mortality when diagnosed, but its incidence and risk factors are poorly understood. We conducted a systematic review and meta-analysis of the cumulative incidence of HCC after Fontan and associated risk factors. METHODS: We searched PubMed, CINAHL, and MEDLINE databases for articles reporting the cumulative incidence of HCC after Fontan operation on March 21, 2023. A single-arm random effects meta-analysis was conducted to assess cumulative incidence at 10, 20, and 30 years after Fontan. Meta-analysis of the difference of the medians was used to assess the influence of risk factors on the development of HCC. RESULTS: Four studies including a total of 1320 patients reported cumulative incidence. The cumulative incidence of HCC at 10, 20, and 30 years after Fontan was 0% (95% CI 0.00-0.01), 2% (0.01-0.06), and 7% (0.03-0.17) respectively. Seven studies including 6,250 patients reported overall incidence of HCC and associated risk factors. At a median 18.4 (IQR 11.9-24.9) years of follow-up, incidence of HCC was 2% (0.01-0.04). Only use of anticoagulation was associated with a lower risk of HCC (RR 0.3, 95% CI 0.1-0.88). DISCUSSION: By 30 years after Fontan, cumulative incidence of HCC is high (7%). Risk of HCC development prior to 10 years post-Fontan is low (0%), though the decision to defer HCC surveillance in this period may require future investigation based on larger studies. Screening with ultrasound every 6 months starting 20 years post-Fontan is reasonable, however, further research regarding timing, cost-effectiveness, additional risk factors associated with HCC risk, and different screening modalities is required.

Circulating Autoantibodies Recognizing Immunodominant Epitopes From Human Apolipoprotein B Associate With Cardiometabolic Risk Factors, but Not With Atherosclerotic Disease.

Rationale: Atherosclerosis is a chronic inflammatory disease of large arteries that involves an autoimmune response with autoreactive T cells and auto-antibodies recognizing Apolipoprotein B (ApoB), the core protein of low-density lipoprotein (LDL). Here, we aimed to establish a clinical association between circulating human ApoB auto-antibodies with atherosclerosis and its clinical risk factors using a novel assay to detect auto-antibodies against a pool of highly immunogenic ApoB-peptides. Methods and Results: To detect polyclonal IgM- and IgG-antibodies recognizing ApoB, we developed a chemiluminescent sandwich ELISA with 30 ApoB peptides selected by an in silico assay for a high binding affinity to MHC-II, which cover more than 80% of known MHC-II variants in a Caucasian population. This pre-selection of immunogenic self-peptides accounted for the high variability of human MHC-II, which is fundamental to allow T cell dependent generation of IgG antibodies. We quantified levels of ApoB-autoantibodies in a clinical cohort of 307 patients that underwent coronary angiography. Plasma anti-ApoB IgG and IgM concentrations showed no differences across healthy individuals (n = 67), patients with coronary artery disease (n = 179), and patients with an acute coronary syndrome (n = 61). However, plasma levels of anti-ApoB IgG, which are considered pro-inflammatory, were significantly increased in patients with obesity (p = 0.044) and arterial hypertension (p < 0.0001). In addition, patients diagnosed with the metabolic syndrome showed significantly elevated Anti-ApoB IgG (p = 0.002). Even when normalized for total plasma IgG, anti-ApoB IgG remained highly upregulated in hypertensive patients (p < 0.0001). We observed no association with triglycerides, total cholesterol, VLDL, or LDL plasma levels. However, total and normalized anti-ApoB IgG levels negatively correlated with HDL. In contrast, total and normalized anti-ApoB IgM, that have been suggested as anti-inflammatory, were significantly lower in diabetic patients (p = 0.012) and in patients with the metabolic syndrome (p = 0.005). Conclusion: Using a novel ELISA method to detect auto-antibodies against ApoB in humans, we show that anti-ApoB IgG associate with cardiovascular risk factors but not with the clinical appearance of atherosclerosis, suggesting that humoral immune responses against ApoB are shaped by cardiovascular risk factors but not disease status itself. This novel tool will be helpful to develop immune-based risk stratification for clinical atherosclerosis in the future.

ApoB-Specific CD4+ T Cells in Mouse and Human Atherosclerosis.

Atherosclerosis is a chronic inflammatory condition of the arterial wall that leads to the formation of vessel-occluding plaques within the subintimal space of middle-sized and larger arteries. While traditionally understood as a myeloid-driven lipid-storage disease, growing evidence suggests that the accumulation of low-density lipoprotein cholesterol (LDL-C) ignites an autoimmune response with CD4+ T-helper (TH) cells that recognize self-peptides from Apolipoprotein B (ApoB), the core protein of LDL-C. These autoreactive CD4+ T cells home to the atherosclerotic plaque, clonally expand, instruct other cells in the plaque, and induce clinical plaque instability. Recent developments in detecting antigen-specific cells at the single cell level have demonstrated that ApoB-reactive CD4+ T cells exist in humans and mice. Their phenotypes and functions deviate from classical immunological concepts of distinct and terminally differentiated TH immunity. Instead, ApoB-specific CD4+ T cells have a highly plastic phenotype, can acquire several, partially opposing and mixed transcriptional programs simultaneously, and transit from one TH subset into another over time. In this review, we highlight adaptive immune mechanisms in atherosclerosis with a focus on CD4+ T cells, introduce novel technologies to detect ApoB-specific CD4+ T cells at the single cell level, and discuss the potential impact of ApoB-driven autoimmunity in atherosclerosis.

Pathogenic Autoimmunity in Atherosclerosis Evolves From Initially Protective Apolipoprotein B100-Reactive CD4+ T-Regulatory Cells.

BACKGROUND: Throughout the inflammatory response that accompanies atherosclerosis, autoreactive CD4+ T-helper cells accumulate in the atherosclerotic plaque. Apolipoprotein B100 (apoB), the core protein of low-density lipoprotein, is an autoantigen that drives the generation of pathogenic T-helper type 1 (TH1) cells with proinflammatory cytokine secretion. Clinical data suggest the existence of apoB-specific CD4+ T cells with an atheroprotective, regulatory T cell (Treg) phenotype in healthy individuals. Yet, the function of apoB-reactive Tregs and their relationship with pathogenic TH1 cells remain unknown. METHODS: To interrogate the function of autoreactive CD4+ T cells in atherosclerosis, we used a novel tetramer of major histocompatibility complex II to track T cells reactive to the mouse self-peptide apo B978-993 (apoB+) at the single-cell level. RESULTS: We found that apoB+ T cells build an oligoclonal population in lymph nodes of healthy mice that exhibit a Treg-like transcriptome, although only 21% of all apoB+ T cells expressed the Treg transcription factor FoxP3 (Forkhead Box P3) protein as detected by flow cytometry. In single-cell RNA sequencing, apoB+ T cells formed several clusters with mixed TH signatures that suggested overlapping multilineage phenotypes with pro- and anti-inflammatory transcripts of TH1, T helper cell type 2 (TH2), and T helper cell type 17 (TH17), and of follicular-helper T cells. ApoB+ T cells were increased in mice and humans with atherosclerosis and progressively converted into pathogenic TH1/TH17-like cells with proinflammatory properties and only a residual Treg transcriptome. Plaque T cells that expanded during progression of atherosclerosis consistently showed a mixed TH1/TH17 phenotype in single-cell RNA sequencing. In addition, we observed a loss of FoxP3 in a fraction of apoB+ Tregs in lineage tracing of hyperlipidemic Apoe-/- mice. In adoptive transfer experiments, converting apoB+ Tregs failed to protect from atherosclerosis. CONCLUSIONS: Our results demonstrate an unexpected mixed phenotype of apoB-reactive autoimmune T cells in atherosclerosis and suggest an initially protective autoimmune response against apoB with a progressive derangement in clinical disease. These findings identify apoB autoreactive Tregs as a novel cellular target in atherosclerosis.

The glycocalyx of human, bovine and murine microvascular endothelial cells cultured in vitro.

This study investigated the morphology and thickness of the glycocalyx linings of microvascular endothelial cells (MVEC). Three distinct cell types were used: the human dermal cells (HDMVEC), the murine cardiac cells (MCMVEC) and the bovine luteal cells (BLMVEC). Cells were cultivated for 48 h. Glycocalyx was stained with ruthenium red and examined under a transmission electron microscope. The glycocalyx of HDMVEC was thin and constant (10-22 nm). No glycocalyx was detected within intracellular vesicles. Two cell populations of MCMVEC were recorded. The minor MCMVEC population was well differentiated and covered with heterogenous glycocalyx (2-200 nm). Conglomerates formed above the baseline along the cell extensions. The major MCMVEC population was undifferentiated and coated by a smooth and thin (12-25 nm) layer of glycocalyx. Intracellular vesicles were also coated with glycocalyx. In the BLMVEC population, 10% had 3-170 nm of discontinuous glycocalyx. Rough conglomerates were observed along cell sprouts. Their intracellular vesicles were coated with glycocalyx. The study found vast differences in the morphology and thickness of endothelial glycocalyx among different MVEC under in vitro cultivation. The only record of active endocytosis was in BLMVEC and MCMVEC. No evidence of active endocytosis was found in HDMVEC.