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Background: CD (cluster of differentiation) 4 + T-cell responses to APOB (apolipoprotein B) are well characterized in atherosclerotic mice and detectable in humans. CD4 + T cells recognize antigenic peptides displayed on highly polymorphic HLA (human leukocyte antigen)-II. Immunogenicity of individual APOB peptides is largely unknown in humans. Only 1 HLA-II-restricted epitope was validated using the DRB1*07:01-APOB 3036 –3050 tetramer. We hypothesized that human APOB may contain discrete immunodominant CD4 + T-cell epitopes that trigger atherosclerosis-related autoimmune responses in donors with diverse HLA alleles. Methods: We selected 20 APOB-derived peptides (APOB 20 ) from an in silico screen and experimentally validated binding to the most commonly occurring human HLA-II alleles. We optimized a restimulation-based workflow to evaluate antigenicity of multiple candidate peptides in HLA-typed donors. This included activation-induced marker assay, intracellular cytokine staining, IFNγ (interferon gamma) enzyme–linked immunospot and cytometric bead array. High-throughput sequencing revealed TCR (T-cell receptor) clonalities of APOB-reactive CD4 + T cells. Results: Using stringent positive, negative, and crossover stimulation controls, we confirmed specificity of expansion-based protocols to detect CD4 + T cytokine responses to the APOB 20 pool. Ex vivo assessment of AIM + CD4 + T cells revealed a statistically significant autoimmune response to APOB 20 but not to a ubiquitously expressed negative control protein, actin. Resolution of CD4 + T responses to the level of individual peptides using IFNγ enzyme–linked immunospot led to the discovery of 6 immunodominant epitopes (APOB 6 ) that triggered robust CD4 + T activation in most donors. APOB 6 -specific responding CD4 + T cells were enriched in unique expanded TCR clonotypes and preferentially expressed memory markers. Cytometric bead array analysis detected APOB 6 -induced secretion of both proinflammatory and regulatory cytokines. In clinical samples from patients with angiographically verified coronary artery disease, APOB 6 stimulation induced higher activation and memory phenotypes and augmented secretion of proinflammatory cytokines TNF (tumor necrosis factor) and IFNγ, compared with patients with low coronary artery disease. Conclusions: Using 3 cohorts, each with ≈20 donors, we discovered and validated 6 immunodominant, HLA-II–restricted APOB epitopes. The immune response to these APOB epitopes correlated with coronary artery disease severity.

Background: B1a and B1b lymphocytes produce IgM that inactivates oxidation-specific epitopes (IgM OSE ) on LDL (low-density lipoprotein) and protects against atherosclerosis. Loss of ID3 (inhibitor of differentiation 3) in B cells selectively promotes B1b but not B1a cell numbers, leading to higher IgM OSE production and reduction in atherosclerotic plaque formation. Yet, the mechanism underlying this regulation remains unexplored. Methods: Bulk RNA sequencing was utilized to identify differentially expressed genes in B1a and B1b cells from Id3 KO and Id3 WT mice. CRISPR/Cas9 and lentiviral genome editing coupled with adoptive transfer were used to identify key Id3 -dependent signaling pathways regulating B1b cell proliferation and the impact on atherosclerosis. Biospecimens from humans with advanced coronary artery disease imaging were analyzed to translate murine findings to human subjects with coronary artery disease. Results: Through RNA sequencing, P62 was found to be enriched in Id3 KO B1b cells. Further in vitro characterization reveals a novel role for P62 in mediating BAFF (B-cell activating factor)-induced B1b cell proliferation through interacting with TRAF6 (tumor necrosis factor receptor 6) and activating NF-κB (nuclear factor kappa B), leading to subsequent C-MYC (C-myelocytomatosis) upregulation. Promoter-reporter assays reveal that Id3 inhibits the E2A protein from activating the P62 promoter. Mice adoptively transferred with B1 cells overexpressing P62 exhibited an increase in B1b cell number and IgM OSE levels and were protected against atherosclerosis. Consistent with murine mechanistic findings, P62 expression in human B1 cells was significantly higher in subjects harboring a function-impairing single nucleotide polymorphism (SNP) at rs11574 position in the ID3 gene and directly correlated with plasma IgM OSE levels. Conclusions: This study unveils a novel role for P62 in driving BAFF-induced B1b cell proliferation and IgM OSE production to attenuate diet-induced atherosclerosis. Results identify a direct role for Id3 in antagonizing E2A from activating the p62 promoter. Moreover, analysis of putative human B1 cells also implicates these pathways in coronary artery disease subjects, suggesting P62 as a new immunomodulatory target for treating atherosclerosis.

Objective:Neovascularization can maintain and even improve tissue perfusion in the setting of limb ischemia during peripheral artery disease. The molecular and cellular mechanisms mediating this process are incompletely understood. We investigate the potential role(s) for Id3 (inhibitor of differentiation 3) in regulating blood flow in a murine model of hindlimb ischemia (HLI).Approach and Results:HLI was modeled through femoral artery ligation and resection and blood flow recovery was quantified by laser Doppler perfusion imaging. Mice with global Id3 deletion had significantly impaired perfusion recovery at 14 and 21 days of HLI. Endothelial- or myeloid cell-specific deletion of Id3 revealed no effect on perfusion recovery while B-cell–specific knockout of Id3 (Id3BKO) revealed a significant attenuation of perfusion recovery. Flow cytometry revealed no differences in ischemia-induced T cells or myeloid cell numbers at 7 days of HLI, yet there was a significant increase in B-1b cells in Id3BKO. Consistent with these findings, ELISA (enzyme-linked immunoassay) demonstrated increases in skeletal muscle and plasma IgM. In vitro experiments demonstrated reduced proliferation and increased cell death when endothelial cells were treated with conditioned media from IgM-producing B-1b cells and tibialis anterior muscles in Id3BKOmice showed reduced density of total CD31+and αSMA+CD31+vessels.Conclusions:This study is the first to demonstrate a role for B-cell–specific Id3 in maintaining blood flow recovery during HLI. Results suggest a role for Id3 in promoting blood flow during HLI and limiting IgM-expressing B-1b cell expansion. These findings present new mechanisms to investigate in peripheral artery disease pathogenesis.

B cell–activating factor (BAFF), part of a tumor necrosis factor family of cytokines, was recently identified as a regulator of atherosclerosis; however, its role in aortic aneurysm has not been determined. Here, the study examined the effect of selective BAFF antagonism using an anti-BAFF antibody (blocks binding of BAFF to receptors BAFF receptor 3, transmembrane activator and CAML interactor, and B-cell maturation antigen) and mBaffR-mFc (blocks binding of BAFF to BAFF receptor 3) on a murine model of abdominal aortic aneurysm (AAA). In a prevention strategy, the antagonists were injected before the induction of AAA, and in an intervention strategy, the antagonists were injected after the induction of AAA. Both strategies attenuated the formation of AAA. In the intervention group, BAFF antagonism depleted most of the mature B-cell subsets in spleen and circulation, leading to enhanced resolution of inflammation in AAA as indicated by decreased infiltration of B cells and proinflammatory macrophages and a reduced number of apoptotic cells. In AAA tissues, B cells and macrophages were found in close contact. In vitro, B cells, irrespective of treatment with BAFF, impaired the efferocytosis activity of macrophages, suggesting a direct innate role of B cells on macrophage function. Altogether, BAFF antagonism affects survival of the mature B cells, promotes resolution of inflammation in the aorta, and attenuates the growth of AAA in mice.

Objective: CD4 T cells are important regulators of atherosclerotic progression. The metabolic profile of CD4 T cells controls their signaling and function, but how atherosclerosis affects T-cell metabolism is unknown. Here, we sought to determine the impact of atherosclerosis on CD4 T-cell metabolism and the contribution of such metabolic alterations to atheroprogression. Approach and Results: Using PCR arrays, we profiled the expression of metabolism genes in CD4 T cells from atherosclerotic apolipoprotein-E knockout mice fed a Western diet. These cells exhibited dysregulated expression of genes critically involved in glycolysis and fatty acid degradation, compared with those from animals fed a standard laboratory diet. We examined how T-cell metabolism was changed in either Western diet–fed apolipoprotein-E knockout mice or samples from patients with cardiovascular disease by measuring glucose uptake, activation, and proliferation in CD4 T cells. We found that naive CD4 T cells from Western diet–fed apolipoprotein-E knockout mice failed to uptake glucose and displayed impaired proliferation and activation, compared with CD4 T cells from standard laboratory diet–fed animals. Similarly, we observed that naive CD4 T-cell frequencies were reduced in the circulation of human subjects with high cardiovascular disease compared with low cardiovascular disease. Naive T cells from high cardiovascular disease subjects also showed reduced proliferative capacity. Conclusions: These results highlight the dysfunction that occurs in CD4 T-cell metabolism and immune responses during atherosclerosis. Targeting metabolic pathways within naive CD4 T cells could thus yield novel therapeutic approaches for improving CD4 T-cell responses against atheroprogression.

Despite the decades-old knowledge that males and people with diabetes mellitus (DM) are at increased risk for coronary artery disease (CAD), the reasons for this association are only partially understood. Among the immune cells involved, recent evidence supports a critical role of T cells as drivers and modifiers of CAD. CD4+ T cells are commonly found in atherosclerotic plaques. We aimed to understand the relationship of CAD with sex and DM by single-cell RNA (scRNA-Seq) and antibody sequencing (CITE-Seq) of CD4+ T cells. Peripheral blood mononuclear cells (PBMCs) of 61 men and women who underwent cardiac catheterization were interrogated by scRNA-Seq combined with 49 surface markers (CITE-Seq). CAD severity was quantified using Gensini scores, with scores above 30 considered CAD+ and below 6 considered CAD−. Four pairs of groups were matched for clinical and demographic parameters. To test how sex and DM changed cell proportions and gene expression, we compared matched groups of men and women, as well as diabetic and non-diabetic subjects. We analyzed 41,782 single CD4+ T cell transcriptomes for sex differences in 16 women and 45 men with and without coronary artery disease and with and without DM. We identified 16 clusters in CD4+ T cells. The proportion of cells in CD4+ effector memory cluster 8 (CD4T8, CCR2+ Em) was significantly decreased in CAD+, especially among DM+ participants. This same cluster, CD4T8, was significantly decreased in female participants, along with two other CD4+ T cell clusters. In CD4+ T cells, 31 genes showed significant and coordinated upregulation in both CAD and DM. The DM gene signature was partially additive to the CAD gene signature. We conclude that (1) CAD and DM are clearly reflected in PBMC transcriptomes, and (2) significant differences exist between women and men and (3) between subjects with DM and non-DM.

Supplemental Digital Content is available in the text., Rationale: Inflammation is a basic component of the pathogenesis of atherosclerosis. CD200 is an immune checkpoint known to control macrophage activation. CD200 recently emerged in the Framingham Heart Study and 2 other cohorts as being potentially relevant in cardiovascular disease. The role of this pathway in cardiovascular disease is unknown. Objective: We sought to examine the role of CD200 in atherosclerosis. Methods and Results: Using hypercholesterolemic apolipoprotein-E deficient mice, we demonstrate that whole-body CD200 deficiency augments atherosclerotic lesion formation and vulnerability. Administration of a CD200-Fusion protein reduces neointima formation. Our data show that the CD200-CD200R pathway restrains activation of CD200R+ lesional macrophages, their production of CCR2 ligands, and monocyte recruitment in vitro and in vivo in an air pouch model. Loss of CD200 leads to an excessive accumulation of classical Ly6Chi monocytes and CCR2+ macrophages within the atherosclerotic aorta, as assessed by mass cytometry. Moreover, we uncover a previously uncharacterized effect of the CD200/CD200R pathway in limiting dysregulated monopoiesis and Ly6Chi monocytosis in hypercholesterolemic mice. Bone marrow chimera experiments demonstrate that the CD200-CD20R pathway enables 2 complementary and tissue-dependent strategies to limit atherogenesis: CD200 expression by bone marrow–derived cells limits systemic monocytosis, while CD200 expression by nonhematopoietic cells, for example, endothelial cells, prevents local plaque growth. We show that CD200R signaling controls monopoiesis and macrophage activation through inhibiting phosphorylation of STAT1 (signal transducer and activator of transcription 1). Finally, CD200R expression on classical monocytes in peripheral blood of patients with coronary artery disease is associated with a lower burden of coronary artery disease and a more favorable Virtual Histology plaque profile. Conclusions: The CD200 checkpoint is a key-limiting factor for monopoiesis, monocyte-macrophage activation, and recruitment in atherosclerosis with conserved features in human and mouse. It thus offers a novel potential therapeutic pathway to treat cardiovascular disease.

Background: Detailed understanding of the immune response to severe acute respiratory syndrome coronavirus (SARS-CoV)-2, the cause of coronavirus disease 2019 (CO­VID-19) has been hampered by a lack of quantitative antibody assays. Objective: The objective was to develop a quantitative assay for IgG to SARS-CoV-2 proteins that could be implemented in clinical and research laboratories. Methods: The biotin-streptavidin technique was used to conjugate SARS-CoV-2 spike receptor-binding domain (RBD) or nucleocapsid protein to the solid phase of the ImmunoCAP. Plasma and serum samples from patients hospitalized with COVID-19 (n = 60) and samples from donors banked before the emergence of COVID-19 (n = 109) were used in the assay. SARS-CoV-2 IgG levels were followed longitudinally in a subset of samples and were related to total IgG and IgG to reference antigens using an ImmunoCAP 250 platform. Results: At a cutoff of 2.5 μg/mL, the assay demonstrated sensitivity and specificity exceeding 95% for IgG to both SARS-CoV-2 proteins. Among 36 patients evaluated in a post-hospital follow-up clinic, median levels of IgG to spike-RBD and nucleocapsid were 34.7 μg/mL (IQR 18–52) and 24.5 μg/mL (IQR 9–59), respectively. Among 17 patients with longitudinal samples, there was a wide variation in the magnitude of IgG responses, but generally the response to spike-RBD and to nucleocapsid occurred in parallel, with peak levels approaching 100 μg/mL, or 1% of total IgG. Conclusions: We have described a quantitative assay to measure IgG to SARS-CoV-2 that could be used in clinical and research laboratories and implemented at scale. The assay can easily be adapted to measure IgG to mutated COVID-19 proteins, has good performance characteristics, and has a readout in standardized units.

Background: Atherosclerosis development in the aorta is region specific with the aortic arch region more prone to disease development than descending thoracic and abdominal aorta. Perivascular adipose tissue (PVAT) directly associates with the aorta, harbors high numbers of B cells, and regulates atherosclerosis development. Age-Associated B cells (ABCs: CD19 + CD11c + ) have recently been reported as a new subset of B cells with unique cell surface and transcriptional signatures. ABCs have been reported to be elevated in autoimmune diseases, where in, these cells have characteristics of auto-antibody producing memory B cells. However, the impact of ABCs in the PVAT near aortic arch and with atherosclerosis progression during aging has not be studied. Methods and Results: To study ABCs in atherosclerosis setting, we used 50- and 100- week old chow diet fed, ApoE KO mice. Flow cytometric analysis showed that there was no difference in frequency of total B cells in the PVAT near the aortic arch region between 50- and 100- week old mice. However, the frequency of ABCs was significantly higher in aortic arch PVAT in 100-week-old mice compared to 50-week-old mice. Additionally, these ABCs in aortic arch PVAT are CD44 + (activation marker) and most ABCs were actively proliferating cells (Ki67 + ), as compared to other CD11c - B cells in 100-week-old ApoE KO mice. Lesion area was measured following Sudan-IV enface staining of aorta and 100-week-old mice developed significantly more disease than the 50-week-old mice. Interestingly, we observed a significant correlation of atherosclerosis disease in aortic arch region with the frequency of ABCs in PVAT near aortic arch (p=0.001, R 2 =0.69). Conclusion: Results provide the first evidence that ABCs in the aortic arch PVAT are highly active and the percentage of these ABCs strongly associates with advanced atherosclerosis disease in aged animals.

Recent work by our group and others have shown individuals with IgE to the oligosaccharide allergen present in mammalian products (α-gal) have increased atheroma burden with increased necrosis and calcification compared to those without α -gal specific IgE. These data suggest α -gal specific IgE increase plaque severity and vulnerability, yet the mechanisms that promote production of IgE to α -gal are unknown. Previous work from our group utilized multi-omics single cell analysis of circulating PBMCs from subjects with coronary angiography at UVA and showed subjects with IgE α -gal sensitization had a higher frequency of CCR6hi switched memory (SWM) B cells and that the CCR6 ligand, CCL20, increased class switching to IgE. To determine mechanisms whereby CCR6 may mediated class switching to IgE, we enriched total B cells from healthy donor peripheral blood mononuclear cells and stimulated with 20ng/ml human IL-4 and 10μg/ml agnostic anti-human CD40 with or without 20ng/ml CCL20 for 3 days. After 3 days of treatment, cells were collected and stained with a 15-color panel and analyzed via flow cytometry. Cells were analyzed for surface expression of CD20 and CD3 to gate total B cells. Gated B cells were further separated into CD27+/IgM-/IgD- to define SWM B cell population. CCL20 treatment did not increase the total percent of SWM B cells; however, there was a 2-3-fold increase in CCR6+ SWM B cells compared to CCR6- SWM B cells. CCL20 treated CCR6+ SWM B cells have an average of 7% increase of phosphorylated mTOR in total SWM B cells compared to nonCCL20 treated CCR6+ SWM B cells. These results suggest CCL20 stimulation induces mTOR phosphorylation and activation. Thus, mTOR activation and downstream mediators may be necessary for α -gal induced B cell class switching. From these preliminary studies, we conclude that CCL20 stimulation increases the percent pmTOR+ SWM B cells. We will continue to investigate downstream mTOR mediators in regard to B cell class switching after CCL20 stimulation and how α-gal sensitization augments B cell IgE class switching and increases atherosclerosis with our novel α -gal-/- Apoe-/- mouse.

TET2 is an epigenetic regulator with an emerging role in regulating CVD severity. TET2 deficiency in mice (TET2 -/- ) was shown to increase atherosclerosis via upregulation of proinflammatory pathways in macrophages. While TET2 has been reported to regulate germinal center formation and class switch recombination in atherogenic B2 cells, its role in atheroprotective B1 cell subsets remains largely unexplored. To investigate the role of TET2 in B1 subsets, flow cytometry of cells from the peritoneal cavity (PEC), spleen and bone marrow of TET2 -/- mice and wildtype littermate controls (n = 14/group) was performed. Results demonstrated increased B1a (p = 0.0162) and B1b (p = 0.0056) cells in TET2 -/- mice in the PEC, their primary niche, but not in the spleen, while in the bone marrow only TET2 -/- B1a cells were increased (p = 0.0021). An enzyme linked immunosorbent assay using the plasma from these mice demonstrated a significant increase in total IgM in the TET2 -/- mice compared to the wildtype mice (p = 0.0287). In addition, sort purified PEC B1a, B1b and B2 cells from TET2 -/- mice and wildtype littermate controls were analyzed for methylation status and RNA expression (n = 24). RNAseq analysis of TET2 -/- PEC B1a, B1b, and B2 cells revealed significantly reduced chemokine receptor CCR6 expression in B1a (-4.88 fold change, 8.03E-08 padj.) and a trending reduction of CCR6 in B1b cells (-2.17 fold change, 0.3477 padj.) compared to wildtype. Further, methylation analysis showed significant hypermethylation of CCR6 in B1a and B1b TET2 -/- cells compared to wildtype. This was corroborated by gene pathway analysis of the RNAseq data which showed significant downregulation of chemotaxis and migration pathways in B1a and B1b TET2 -/- cells. We conclude that loss of TET2 increases hypermethylation of CCR6 and suppresses CCR6 RNA expression in B1 cells which may impair trafficking out of the PEC to the spleen, but not necessarily the bone marrow, leading to PEC accumulation of B1 subtypes and an increase in the total plasma level of atheroprotective IgM. Further study is needed to identify mechanisms of potential B1 cell-mediated atheroprotection in the case of TET2 loss.

Supplemental Digital Content is available in the text., Background: Rupture and erosion of advanced atherosclerotic lesions with a resultant myocardial infarction or stroke are the leading worldwide cause of death. However, we have a limited understanding of the identity, origin, and function of many cells that make up late-stage atherosclerotic lesions, as well as the mechanisms by which they control plaque stability. Methods: We conducted a comprehensive single-cell RNA sequencing of advanced human carotid endarterectomy samples and compared these with single-cell RNA sequencing from murine microdissected advanced atherosclerotic lesions with smooth muscle cell (SMC) and endothelial lineage tracing to survey all plaque cell types and rigorously determine their origin. We further used chromatin immunoprecipitation sequencing (ChIP-seq), bulk RNA sequencing, and an innovative dual lineage tracing mouse to understand the mechanism by which SMC phenotypic transitions affect lesion pathogenesis. Results: We provide evidence that SMC-specific Klf4- versus Oct4-knockout showed virtually opposite genomic signatures, and their putative target genes play an important role regulating SMC phenotypic changes. Single-cell RNA sequencing revealed remarkable similarity of transcriptomic clusters between mouse and human lesions and extensive plasticity of SMC- and endothelial cell-derived cells including 7 distinct clusters, most negative for traditional markers. In particular, SMC contributed to a Myh11-, Lgals3+ population with a chondrocyte-like gene signature that was markedly reduced with SMC-Klf4 knockout. We observed that SMCs that activate Lgals3 compose up to two thirds of all SMC in lesions. However, initial activation of Lgals3 in these cells does not represent conversion to a terminally differentiated state, but rather represents transition of these cells to a unique stem cell marker gene–positive, extracellular matrix-remodeling, “pioneer” cell phenotype that is the first to invest within lesions and subsequently gives rise to at least 3 other SMC phenotypes within advanced lesions, including Klf4-dependent osteogenic phenotypes likely to contribute to plaque calcification and plaque destabilization. Conclusions: Taken together, these results provide evidence that SMC-derived cells within advanced mouse and human atherosclerotic lesions exhibit far greater phenotypic plasticity than generally believed, with Klf4 regulating transition to multiple phenotypes including Lgals3+ osteogenic cells likely to be detrimental for late-stage atherosclerosis plaque pathogenesis.

The immune system plays an important role in obesity-induced adipose tissue inflammation and the resultant metabolic dysfunction, which can lead to hypertension, dyslipidemia, and insulin resistance and their downstream sequelae of type 2 diabetes mellitus and cardiovascular disease. While macrophages are the most abundant immune cell type in adipose tissue, other immune cells are also present, such as B cells, which play important roles in regulating adipose tissue inflammation. This brief review will overview B-cell subsets, describe their localization in various adipose depots and summarize our knowledge about the function of these B-cell subsets in regulating adipose tissue inflammation, obesity-induced metabolic dysfunction and atherosclerosis.

Macrophages are important regulators of obesity-associated inflammation and PPARα and -γ agonism in macrophages has anti-inflammatory effects. In this study, we tested the efficacy with which liposomal delivery could target the PPARα/γ dual agonist tesaglitazar to macrophages while reducing drug action in common sites of drug toxicity: the liver and kidney, and whether tesaglitazar had anti-inflammatory effects in an in vivo model of obesity-associated dysmetabolism. Methods: Male leptin-deficient (ob/ob) mice were administered tesaglitazar or vehicle for one week in a standard oral formulation or encapsulated in liposomes. Following the end of treatment, circulating metabolic parameters were measured and pro-inflammatory adipose tissue macrophage populations were quantified by flow cytometry. Cellular uptake of liposomes in tissues was assessed using immunofluorescence and a broad panel of cell subset markers by flow cytometry. Finally, PPARα/γ gene target expression levels in the liver, kidney, and sorted macrophages were quantified to determine levels of drug targeting to and drug action in these tissues and cells. Results: Administration of a standard oral formulation of tesaglitazar effectively treated symptoms of obesity-associated dysmetabolism and reduced the number of pro-inflammatory adipose tissue macrophages. Macrophages are the major cell type that took up liposomes with many other immune and stromal cell types taking up liposomes to a lesser extent. Liposome delivery of tesaglitazar did not have effects on inflammatory macrophages nor did it improve metabolic parameters to the extent of a standard oral formulation. Liposomal delivery did, however, attenuate effects on liver weight and liver and kidney expression of PPARα and -γ gene targets compared to oral delivery. Conclusions: These findings reveal for the first time that tesaglitazar has anti-inflammatory effects on adipose tissue macrophage populations in vivo. These data also suggest that while nanoparticle delivery reduced off-target effects, yet the lack of tesaglitazar actions in non-targeted cells such (as hepatocytes and adipocytes) and the uptake of drug-loaded liposomes in many other cell types, albeit to a lesser extent, may have impacted overall therapeutic efficacy. This fulsome analysis of cellular uptake of tesaglitazar-loaded liposomes provides important lessons for future studies of liposome drug delivery.

Murine B-1 cells produce IgMs that inactivate oxidation-specific epitopes and protect against atherosclerosis. Despite compelling data that IgM to MDA-LDL (IgM MDA-LDL ) is inversely associated with coronary artery disease (CAD) and cardiovascular (CV) events in human, the human B cell subtype that produces IgM MDA-LDL is unknown. Here, we utilized mass cytometry to identify the 11 circulating human B cell subtypes and discovered that only the frequency of CD20 + CD27 + IgM + cells was associated with IgM MDA-LDL levels. Notably, high expression of CD24, a GPI-anchored sialoglycoprotein, was associated with IgM MDA-LDL (r = 0.57, p = 0.002) and inversely associated with CAD severity (r = -0.58, p=0.001). Adoptive transfer (AT) of sorted CD20 + CD27 + IgM + CD24hi (B 27+IgM+CD24hi ) and CD24lo/- (B 27+IgM+CD24lo/- ) human B cells into humanized mice demonstrated that CD24 is critical for trafficking to the spleen and IgM production. Bulk RNAseq coupled with pathway analysis of B 27+IgM+CD24hi and B 27+IgM+CD24lo/- cells revealed enhanced BCR and CCR6 signaling in B 27+IgM+CD24hi . Imaging flow cytometry indicated colocalization between CD24 and CCR6 which was abrogated by CD24 blocking antibody (CD24mAb). Trans-well migration and internalization assays demonstrated that CD24 blockade increased CCL20-induced CCR6 internalization (p < 0.05, n =4), and reduced CCL20-induced migration of B 27+IgM+CD24hi cells (p < 0.05, n =4). CD24mAb treatment of B 27+IgM+CD24hi cells prior to AT into humanized mice also reduced the amount of surface CCR6 on B 27+IgM+CD24hi cells in vivo (p < 0.05, n = 4). Both CCR6 knockout and CD24 inhibition of B 27+IgM+CD24hi cells reduced migration to the spleen (p < 0.05, n = 4), and plasma level of human IgM (p = 0.057, n = 4). Lastly, single cell multi-omics sequencing of PBMCs from 60 CAD subjects revealed elevated CCR6 and IgM signaling in B 27+IgM+CD24hi cells in subjects with less severe CAD. Results provide the first evidence for a role for CD24 in regulating CCR6-mediated B cell homing to the spleen, IgM production and CAD in humans. Findings may have important implications for the new CD24 immunotherapy entering clinical trials and raise the possibility that augmenting CD24 and/or CCR6 on B 27+IgM+ cells may be an effective atheroprotective strategy.

Background: The co-stimulatory CD40-CD40L dyad is an important driver of atherosclerosis. CD40 exerts divergent, cell-specific roles, which differentially impacts atherogenesis. Objectives: We here investigate the role of the most prominent CD40-expressing cell type, the CD40 + B cell, in atherosclerosis. Methods: B cell subset specific CD40-expression of patients with mild and severe coronary artery disease (CAD) was determined by mass-cytometry and correlated to CAD severity. Underlying mechanisms were revealed using CD19-CD40 flfl -ApoE -/- (CD40 BKO ) and CD40 flfl -ApoE -/- (CD40 BWT ) mice. Results: Patients with severe CAD had similar CD40 expression levels on most B cell subsets but showed a profound decrease in CD40 on B1 cells. This was associated with increased atherosclerotic plaque burden and decreased plaque fibrosis. Likewise, CD40 BKO mice exhibited an increased plaque area and a more advanced stage of atherosclerosis. Absence of B cell CD40 caused a decrease in immunoglobulin (Ig) producing cells, including germinal center-, plasma-, but especially B1 cells, thereby reducing levels of (anti-ox/MDA-LDL) IgM and (anti-ox/MDA-LDL) IgG. Interestingly, transcriptomics analysis revealed that the absence of CD40 on B1b cells in particular, caused altered gene expression pathways related to lipid uptake ( Cd36, Ldlr ), cellular stress and metabolism ( Nr4a1, Hif1a ), and cell death ( Naip5/6, Top1 ). Indeed, in vitro analysis showed that B1b CD40KO cells took up excessive amounts of ac/oxLDL, exhibited defective BCR signaling, and were prone to apoptosis, especially in hyperlipidemic conditions. Finally, transfer of wild-type B1b cells into CD40 BKO mice prevented the increase in atherosclerosis. Conclusions: We here show that CD40 is a critical modulator of B1 cell protective function in hypercholesterolemia and atherosclerosis.

Atherosclerosis is associated with increased lipid peroxidation, leading to generation of multiple oxidation-specific epitopes (OSEs), contributing to the pathogenesis of atherosclerosis and its clinical manifestation. Oxidized cholesteryl esters (OxCEs) are a major class of OSEs found in human plasma and atherosclerotic tissue. To evaluate OxCEs as a candidate biomarker, we generated a novel mouse monoclonal Ab (mAb) specific to an OxCE modification of proteins. The mAb AG23 (IgG1) was raised in C57BL6 mice immunized with OxCE-modified keyhole limpet hemocyanin, and hybridomas were screened against OxCE-modified BSA. This method ensures mAb specificity to the OxCE modification, independent of a carrier protein. AG23 specifically stained human carotid artery atherosclerotic lesions. An ELISA method, with AG23 as a capture and either anti-apoAI or anti-apoB-100 as the detection Abs, was developed to assay apoAI and apoB-100 lipoproteins that have one or more OxCE epitopes. OxCE-apoA or OxCE-apoB did not correlate with the well-established oxidized phospholipid-apoB biomarker. In a cohort of subjects treated with atorvastatin, OxCE-apoA was significantly lower than in the placebo group, independent of the apoAI levels. These results suggest the potential diagnostic utility of a new biomarker assay to measure OxCE-modified lipoproteins in patients with CVD.

Supplemental Digital Content is available in the text., Objective: Few studies of population-based cohorts have investigated prospective associations of lymphoid and myeloid cell subsets in cardiovascular disease onset and progression. The purpose of this analysis was to determine associations of prespecified myeloid and lymphoid lineage cell subsets with common carotid artery intima-media thickness (IMT) progression. Approach and Results: We performed a prospective case-cohort study of 1195 participants from the Multi-Ethnic Study of Atherosclerosis who had peripheral blood mononuclear cells stored from the baseline examination. Key exposure variables were prespecified subsets of lymphoid and myeloid lineage immune cells, phenotyped by multicolor flow cytometry. The primary outcome was progression from baseline (Exam 1) to year 10 (Exam 5) in common carotid IMT. Higher proportions of nonclassical monocytes (CD14dimCD16++) were significantly associated with IMT progression over 10 years, but classical monocytes (CD14++CD16−), CD4+CD28− T cells, and T helper cells producing IL-17 (interleukin 17; T helper 17 cells) were not associated with significant changes in IMT over 10 years. There were significant interactions between monocyte subsets and sex with respect to IMT progression: in sex-stratified analyses, nonclassical monocytes were associated with significant IMT progression and classical monocytes were associated with significant IMT regression for men, whereas there were no significant associations of monocyte subsets with IMT change for women. Conclusions: Nonclassical monocytes were associated with progression of carotid IMT. There were significant sex differences in associations of monocyte subsets with IMT progression: for men, nonclassical monocytes were associated with IMT progression and classical monocytes were associated with regression, whereas these associations were null for women.

IL-1β is a key mediator of the cytokine storm linked to high morbidity and mortality from COVID-19 and IL-1β blockade with Anakinra and Canakinumab during COVID-19 infection has entered clinical trials. Using mass cytometry of human peripheral blood mononuclear cells, we identified effector memory CD4(+) T cells and CD4(-)CD8(low/-)CD161(+) T cells, specifically those positive for the chemokine receptor CCR6, as the circulating immune subtypes with the greatest response to IL-1β. This response manifested as increased phosphorylation and thus activation of the proinflammatory transcription factor NF-κB and was also seen in other subsets, including CD11c(+) myeloid dendritic cells, classical monocytes, two subsets of natural killer cells (CD16(-)CD56(bright)CD161(-) and CD16(-)CD56(dim)CD161(+)), and lineage(-) (Lin(-)) cells expressing CD161 and CD25. IL-1β also induced a rapid but less robust increase in the phosphorylation of the kinase p38 as compared to that of NF-κB in most of these immune cell subsets. Prolonged IL-1β stimulation increased the phosphorylation of the transcription factor STAT3 and to a lesser extent that of STAT1 and STAT5 across various immune cell types. IL-1β-induced production of IL-6 likely led to the activation of STAT1 and STAT3 at later time points. Interindividual heterogeneity and inhibition of STAT activation by Anakinra raises the possibility that assays measuring NF-κB phosphorylation in response to IL-1β in CCR6(+) T cell subtypes could identify those patients at higher risk of cytokine storm and most likely to benefit from IL-1β-neutralizing therapies.

Objective: The aim of this study was to unravel mechanisms whereby deficiency of the transcription factor Id3 (inhibitor of differentiation 3) leads to metabolic dysfunction in visceral obesity. We investigated the impact of loss of Id3 on hyaluronic acid (HA) production by the 3 HAS isoenzymes (HA synthases; -1, -2, and -3) and on obesity-induced adipose tissue (AT) accumulation of proinflammatory B cells. Approach and Results: Male Id3 −/− mice and respective wild-type littermate controls were fed a 60% high-fat diet for 4 weeks. An increase in inflammatory B2 cells was detected in Id3 −/− epididymal AT. HA accumulated in epididymal AT of high-fat diet–fed Id3 −/− mice and circulating levels of HA were elevated. Has2 mRNA expression was increased in epididymal AT of Id3 −/− mice. Luciferase promoter assays showed that Id3 suppressed Has2 promoter activity, while loss of Id3 stimulated Has2 promoter activity. Functionally, HA strongly promoted B2 cell adhesion in the AT and on cultured vascular smooth muscle cells of Id3 −/− mice, an effect sensitive to hyaluronidase. Conclusions: Our data demonstrate that loss of Id3 increases Has2 expression in the epididymal AT, thereby promoting HA accumulation. In turn, elevated HA content promotes HA-dependent binding of B2 cells and an increase in the B2 cells in the AT, which contributes to AT inflammation.

TET2 is an evolutionarily conserved dioxygenase that catalyzes the conversion of 5-methyl-cytosine to 5- hydroxymethyl-cytosine, promotes DNA demethylation and regulates transcription. TET2 has been reported to regulate germinal center formation and class switch recombination in B2 B cells, yet its role in B1 B cell subsets remains largely unexplored. To investigate the role of TET2 in B1 subsets, flow cytometry of cells from the peritoneal cavity (PEC), spleen and bone marrow of TET2−/− mice and wildtype littermate controls (n = 14/group) was performed. In addition, sort purified PEC B1a, B1b and B2 cells were analyzed for methylation status (n = 24) and RNA expression (n = 24). Results demonstrated increased B1a (p = 0.0162) and B1b (p = 0.0056) cells in TET2−/− mice in the PEC, their primary niche, but not in the spleen, while in the bone marrow only TET2−/− B1a cells were increased (p = 0.0021). RNAseq analysis of PEC B1a, B1b, and B2 cells from TET2−/− and wildtype mice revealed reduced chemokine receptor CCR6 expression in B1a (−4.879068141 fold change, 1. 8.03E-08 padj.) and B1b cells (−2.17044776 fold change, 0.34771255 padj.) from the TET2−/− mice. Further, methylation analysis showed significant hypermethylation of CCR6 in B1a and B1b TET2−/− cells compared to wildtype B1a and B1b cells. This was corroborated by gene pathway analysis of the RNAseq data which showed significant downregulation of chemotaxis and migration pathways in B1a and B1b TET2−/− cells. We conclude that loss of TET2 increases hypermethylation of CCR6 and suppresses CCR6 RNA expression in B1 cells which may impair trafficking out of the PEC to the spleen, but not necessarily the bone marrow, leading to PEC accumulation of B1 subtypes. Supported by grants from the NIH: 1R01HL 136098-01 (McNamara, C PI), R01 HL141123 (McNamara, C PI), T32 HL007284 (Dennis, E)

Background: Machine learning (ML) has emerged as a powerful approach for predicting outcomes based on patterns and inferences. Improving prediction of severe coronary artery disease (CAD) has the potential for personalizing prevention and treatment strategies and for identifying individuals that may benefit from cardiac catheterization. We developed a novel ML approach combining traditional cardiac risk factors (CRF) with a single nucleotide polymorphism (SNP) in a gene associated with human CAD (ID3 rs11574) to enhance prediction of CAD severity, Methods: ML models incorporating CRF along with ID3 genotype at rs11574 were evaluated. The most predictive model, a deep neural network, was used to classify patients into high (&gt, 32) and low level (&le, 32) Gensini severity score. This model was trained on 325 and validated on 82 patients. Prediction performance of the model was summarized by a confusion matrix and area under the receiver operating characteristics curve (ROC-AUC), and Results: Our neural network predicted severity score with 81% and 87% accuracy for the low and the high groups respectively with an ROC-AUC of 0.84 for 82 patients in the test group. The addition of ID3 rs11574 to CRF significantly enhanced prediction accuracy from 65% to 81% in the low group, and 72% to 84% in the high group. Age, high-density lipoprotein (HDL), and systolic blood pressure were the top 3 contributors in predicting severity score, Conclusions: Our neural network including ID3 rs11574 improved prediction of CAD severity over use of Framingham score, which may potentially be helpful for clinical decision making in patients at increased risk of complications from coronary angiography.

Background: Atherosclerotic plaques in mice and humans contain natural killer (NK) cells. Data on the role of NK cells in atherosclerosis using different transgenic mice models is inconsistent. Some studies showed that NK cells augment atherosclerosis through their cytotoxic potential, while others reported no effect. Evidence in humans indicates that NK cells are atherogenic. Frequency of NK cells and expression of the activating NK cell receptors are associated with severe disease and symptomatic carotid atherosclerotic plaques in humans. Hypothesis: We tested if coronary artery disease (CAD) subjects with necrotic plaques have a higher frequency of the circulating NK cells. Methods: We performed mass cytometry on peripheral blood mononuclear cells from matched CAD subjects with low and high (n=9 each) necrotic plaque content as determined by intravascular ultrasound-virtual histology. Results: CAD subjects with high necrotic plaques have significantly higher atheroburden, stenosis, calcium, fatty plaque content, and lower plaque fibrosis. Interestingly, CAD subjects with high necrotic plaques exhibited a significantly higher frequency of the CD56 bright NK cells as compared to those with low necrotic plaques (4.618 ± 0.625 vs 2.481 ± 0.37; p=0.011). Moreover, frequency of CD25 + NK cells also trended to be higher in subjects with high necrotic plaques. The frequency of the cytotoxic CD56 dim NK cells did not differ between the two groups. Correlation analyses demonstrated a significant positive association of CD56 bright NK cells with atheroburden (r=0.43; p=0.04), stenosis (r=0.58; p=0.005), plaque necrotic (r=0.71; p=0.002), calcium contents (r=0.73; p=0.0001), and a negative association with the plaque fibrous content (r=0.71; p= 0.0003). CD25 + NK cells also showed similar trending associations with burden, stenosis and plaque features. Conclusions: Our data provides yet another evidence of the atherogenic role of NK cells in humans and indicates that the CD56 bright NK cells may contribute to the development of a vulnerable plaque. CD56 bright NK cells produce proinflammatory cytokines including IFN-γ and TNF-α and cytotoxic enzymes that may contribute to increased inflammation, cell activation, and apoptosis within the plaque.

BackgroundDetailed understanding of the immune response to SARS-CoV-2, the cause of coronavirus disease 2019 (COVID-19), has been hampered by a lack of quantitative antibody assays.ObjectiveTo develop a quantitative assay for IgG to SARS-CoV-2 proteins that could readily be implemented in clinical and research laboratories.MethodsThe biotin-streptavidin technique was used to conjugate SARS-CoV-2 spike receptor-binding-domain (RBD) or nucleocapsid protein to the solid-phase of the ImmunoCAP resin. Plasma and serum samples from patients with COVID-19 (n=51) and samples from donors banked prior to the emergence of COVID-19 (n=109) were used in the assay. SARS-CoV-2 IgG levels were followed longitudinally in a subset of samples and were related to total IgG and IgG to reference antigens using an ImmunoCAP 250 platform.ResultsPerformance characteristics demonstrated 100% sensitivity and 99% specificity at a cut-off level of 2.5 µg/mL for both SARS-CoV-2 proteins. Among 36 patients evaluated in a post-hospital follow-up clinic, median levels of IgG to spike-RBD and nucleocapsid were 34.7 µg/mL (IQR 18-52) and 24.5 µg/mL (IQR 9-59), respectively. Among 17 patients with longitudinal samples there was a wide variation in the magnitude of IgG responses, but generally the response to spike-RBD and to nucleocapsid occurred in parallel, with peak levels approaching 100 µg/mL, or 1% of total IgG.ConclusionsWe have described a quantitative assay to measure IgG to SARS-CoV-2 that could be used in clinical and research laboratories and implemented at scale. The assay can easily be adapted to measure IgG to novel antigens, has good performance characteristics and a read-out in standardized units.

The diverse leukocyte infiltrate in atherosclerotic mouse aortas was recently analyzed in 9 single-cell RNA sequencing and 2 mass cytometry studies. In a comprehensive meta-analysis, we confirm 4 known macrophage subsets—resident, inflammatory, interferon-inducible cell, and Trem2 (triggering receptor expressed on myeloid cells-2) foamy macrophages—and identify a new macrophage subset resembling cavity macrophages. We also find that monocytes, neutrophils, dendritic cells, natural killer cells, innate lymphoid cells-2, and CD (cluster of differentiation)-8 T cells form prominent and separate immune cell populations in atherosclerotic aortas. Many CD4 T cells express IL (interleukin)-17 and the chemokine receptor CXCR (C-X-C chemokine receptor)-6. A small number of regulatory T cells and T helper 1 cells is also identified. Immature and naive T cells are present in both healthy and atherosclerotic aortas. Our meta-analysis overcomes limitations of individual studies that, because of their experimental approach, over- or underrepresent certain cell populations. Mass cytometry studies demonstrate that cell surface phenotype provides valuable information beyond the cell transcriptomes. The present analysis helps resolve some long-standing controversies in the field. First, Trem2 + foamy macrophages are not proinflammatory but interferon-inducible cell and inflammatory macrophages are. Second, about half of all foam cells are smooth muscle cell-derived, retaining smooth muscle cell transcripts rather than transdifferentiating to macrophages. Third, Pf4 , which had been considered specific for platelets and megakaryocytes, is also prominently expressed in the main population of resident vascular macrophages. Fourth, a new type of resident macrophage shares transcripts with cavity macrophages. Finally, the discovery of a prominent innate lymphoid cell-2 cluster links the single-cell RNA sequencing work to recent flow cytometry data suggesting a strong atheroprotective role of innate lymphoid cells-2. This resolves apparent discrepancies regarding the role of T helper 2 cells in atherosclerosis based on studies that predated the discovery of innate lymphoid cells-2 cells.

Cryopreserved peripheral blood mononuclear cells (PBMCs) are frequently collected and provide disease- and treatment-relevant data in clinical studies. Here, we developed combined protein (40 antibodies) and transcript single cell (sc)RNA sequencing in PBMCs. Among 31 participants in the WIHS Study, we sequenced 41,611 cells. Using Boolean gating followed by Seurat UMAPs and Louvain clustering, we identified 58 subsets among CD4 T, CD8 T, B, NK cells and monocytes. This resolution was superior to flow cytometry, mass cytometry or scRNA-sequencing without antibodies. Since the transcriptome was not needed for cell identification, combined protein and transcript scRNA-Seq allowed for the assessment of disease-related changes in transcriptomes and cell type proportion. As a proof-of-concept, we showed such differences between healthy and matched individuals living with HIV with and without cardiovascular disease. In conclusion, combined protein and transcript scRNA sequencing is a suitable and powerful method for clinical investigations using PBMCs.

Background/objectives The incidence of obesity continues to increase worldwide and while the underlying pathogenesis remains largely unknown, nutrient excess, manifested by “Westernization” of the diet and reduced physical activity have been proposed as key contributing factors. Western-style diets, in addition to higher caloric load, are characterized by excess of advanced glycation end products (AGEs), which have been linked to the pathophysiology of obesity and related cardiometabolic disorders. AGEs can be “trapped” in adipose tissue, even in the absence of diabetes, in part due to higher expression of the receptor for AGEs (RAGE) and/or decreased detoxification by the endogenous glyoxalase (GLO) system, where they may promote insulin resistance. It is unknown whether the expression levels of genes linked to the RAGE axis, including AGER (the gene encoding RAGE), Diaphanous 1 (DIAPH1), the cytoplasmic domain binding partner of RAGE that contributes to RAGE signaling, and GLO1 are differentially regulated by the degree of obesity and/or how these relate to inflammatory and adipocyte markers and their metabolic consequences. Subjects/methods We sought to answer this question by analyzing gene expression patterns of markers of the AGE/RAGE/DIAPH1 signaling axis in abdominal subcutaneous (SAT) and omental (OAT) adipose tissue from obese and morbidly obese subjects. Results In SAT, but not OAT, expression of AGER was significantly correlated with that of DIAPH1 (n = 16; $$\hat \beta = 0.719$$ β ̂ = 0.719 , [0.260, 1.177]; q = 0.008) and GLO1 (n = 16; $$\hat \beta = 0.773$$ β ̂ = 0.773 , [0.364, 1.182]; q = 0.004). Furthermore, in SAT, but not OAT, regression analyses revealed that the expression pattern of genes in the AGE/RAGE/DIAPH1 axis is strongly and positively associated with that of inflammatory and adipogenic markers. Remarkably, particularly in SAT, not OAT, the expression of AGER positively and significantly correlated with HOMA-IR (n = 14; $$\hat \beta = 0.794$$ β ̂ = 0.794 , [0.338, 1.249]; q = 0.018). Conclusions These observations suggest associations of the AGE/RAGE/DIAPH1 axis in the immunometabolic pathophysiology of obesity and insulin resistance, driven, at least in part, through expression and activity of this axis in SAT.

There is a growing interest in using liposomes to deliver compounds in vivo particularly for targeted treatment approaches. Depending on the liposome formulation, liposomes may be preferentially taken up by different cell types in the body. This may influence the efficacy of the therapeutic particle as progression of different diseases is tissue- and cell-type-specific. In this protocol, we present one method for synthesizing and fluorescently labeling liposomes using DSPC, cholesterol, and PEG-2000 DSPE and the lipid dye DiD as a fluorescent label. This protocol also presents an approach for delivering liposomes in vivo and assessing cell-specific uptake of liposomes using flow cytometry. This approach can be used to determine the types of cells that take up liposomes and quantify the distribution and proportion of liposome-uptake across cell types and tissues. While not mentioned in this protocol, additional assays such as immunofluorescence and single-cell fluorescence imaging on a cytometer will strengthen any findings or conclusions made as they permit assessment of intracellular staining. Protocols may also need to be adapted depending on the tissue(s) of interest.

As cell function is influenced by niche-specific factors in the cellular microenvironment, methods to dissect cell localization and migration can provide further insight on cell function. B-1a cells are a unique B cell subset in mice that produce protective natural IgM antibodies against oxidation-specific epitopes that arise during health and disease. B-1a cell IgM production differs depending on B-1a cell location, and therefore it becomes useful from a therapeutic standpoint to target B-1a localization to niches supportive of high antibody production. Here we describe a method to target B-1a cell migration to the bone marrow by retroviral-mediated overexpression of the C-X-C motif chemokine receptor 4 (CXCR4). Gene induction in primary murine B cells can be challenging and typically yields low transfection efficiencies of 10-20% depending on technique. Here we demonstrate that retroviral transduction of primary murine B-1a cells results in 30-40% transduction efficiency. This method utilizes adoptive cell transfer of transduced B-1a cells into B cell-deficient recipient mice so that donor B-1a cell migration and localization can be visualized. This protocol can be modified for other retroviral constructs and can be used in diverse functional assays post-adoptive transfer, including analysis of donor cell or host cell phenotype and function, or analysis of soluble factors secreted post B-1a cell transfer. The use of distinct donor and recipient mice differentiated by CD45.1 and CD45.2 allotype and the presence of a GFP reporter within the retroviral plasmid could also enable detection of donor cells in other, immune-sufficient mouse models containing endogenous B cell populations.

IL-1β has emerged as a key mediator of the cytokine storm linked to high morbidity and mortality from COVID-19 and blockade of the IL-1 receptor (IL-1R) with Anakinra has entered clinical trials in COVID-19 subjects. Yet, knowledge of the specific immune cell subsets targeted by IL-1β and IL-1β-induced signaling pathways in humans is limited. Utilizing mass cytometry (CyTOF) of human peripheral blood mononuclear cells, we identified effector memory CD4 T cells and CD4−CD8low/-CD161+ T cells as the circulating immune subtypes with the greatest expression of p-NF-κB in response to IL-1β stimulation. Notably, CCR6 distinctly identified T cells most responsive to IL-1β. Other subsets including CD11c myeloid dendritic cells (mDCs), classical monocytes (CM), two subsets of natural killer cells (CD16−CD56brightCD161− and CD16−CD56dimCD161+) and a population of lineage−(Lin-) cells expressing CD161 and CD25 also showed IL-1β-induced expression of p-NF-kB. The IL-1R antagonist, Anakinra significantly inhibited IL-1β-induced p-NF-kB in the CCR6+ T cells and CD11c mDCs with a trending inhibition in CD14 monocytes and Lin−CD161+CD25+ cells. IL-1β also induced a rapid but much less robust increase in p-p38 expression as compared to p-NF-kB in the majority of these same immune cell subsets. Prolonged IL-1β stimulation greatly increased p-STAT3 and to a much lesser extent p-STAT1 and p-STAT5 in T cell subsets, monocytes, DCs and the Lin−CD161+CD25+ cells suggesting IL-1β-induced production of downstream STAT-activating cytokines, consistent with its role in cytokine storm. Interindividual heterogeneity and inhibition of this activation by Anakinra raises the intriguing possibility that assays to measure IL-1β-induced p-NF-kB in CCR6+ T cell subtypes could identify those at higher risk of cytokine storm and those most likely to benefit from Anakinra therapy.

Objective Peroxisome proliferator-activated receptors (PPARs) are key transcription factors that regulate adipose development and function, and the conversion of white into brown-like adipocytes. Here we investigated whether PPARα and PPARγ activation synergize to induce the browning of white fat. Methods A selection of PPAR activators was tested for their ability to induce the browning of both mouse and human white adipocytes in vitro, and in vivo in lean and obese mice. Results All dual PPARα/γ activators tested robustly increased uncoupling protein 1 (Ucp1) expression in both mouse and human adipocytes in vitro, with tesaglitazar leading to the largest Ucp1 induction. Importantly, dual PPARα/γ activator tesaglitazar strongly induced browning of white fat in vivo in both lean and obese male mice at thermoneutrality, greatly exceeding the increase in Ucp1 observed with the selective PPARγ activator rosiglitazone. While selective PPARγ activation was sufficient for the conversion of white into brown-like adipocytes in vitro, dual PPARα/γ activation was superior to selective PPARγ activation at inducing white fat browning in vivo. Mechanistically, the superiority of dual PPARα/γ activators is mediated at least in part via a PPARα-driven increase in fibroblast growth factor 21 (FGF21). Combined treatment with rosiglitazone and FGF21 resulted in a synergistic increase in Ucp1 mRNA levels both in vitro and in vivo. Tesaglitazar-induced browning was associated with increased energy expenditure, enhanced insulin sensitivity, reduced liver steatosis, and an overall improved metabolic profile compared to rosiglitazone and vehicle control groups. Conclusions PPARγ and PPARα synergize to induce robust browning of white fat in vivo, via PPARγ activation in adipose, and PPARα-mediated increase in FGF21., Graphical abstract Dual PPARα/γ activation is superior to selective PPARγ activation at inducing browning of white fat in vivo: via PPARγ action in the adipose and a PPARα-mediated action in the liver resulting in increased circulating fibroblast growth factor 21 (FGF21).Image 1, Highlights • Dual PPARα/γ activators robustly induce browning of white fat in vitro and in vivo. • PPARγ action alone is sufficient to convert white into brown-like adipocytes in vitro. • Dual PPARα/γ activators are superior to PPARγ activators for browning of white fat in vivo. • PPARγ action in adipose and PPARα-mediated increase in FGF21 synergize to induce browning of white fat in vivo.