B1b cell homeostasis is maintained by CD40 in atherosclerosis

Background: The co-stimulatory CD40-CD40L dyad is an important driver of atherosclerosis. CD40 exerts divergent, cell-specific roles, which differentially impact atherogenesis. Objectives: We here investigate the role of the most prominent CD40-expressing cell-type, the 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 elucidated using B-cell CD40-deficient CD19Cre-CD40flfl-ApoE-/-(CD40BKO) mice and control littermates (CD40BWT). Results: Patients with severe CAD had similar CD40 expression levels on most B-cell subsets but showed a profound decrease in CD40 on putative B1 cells. This was associated with increased atherosclerotic plaque burden and decreased plaque fibrosis. Likewise, CD40BKO mice exhibited an increased plaque area and more advanced staging of atherosclerosis. Absence of CD40 on B-cells caused a decrease in immunoglobulin (Ig) producing cells, including germinal center-, plasma-, but especially B1 cells, thereby reducing levels of (anti-ox/MDA-LDL) IgG and protective (anti-ox/MDA-LDL) IgM. Transcriptomics analysis revealed that the absence of CD40 on B1b cells caused altered gene expression pathways related to lipid uptake (Cd36, Ldlr), cellular stress and metabolism (Nr4a1, Hif1a), and cell death (Naip5/6, Ccnd2). Indeed, in vitro analysis showed that B1bCD40KO cells took up excessive amounts of ac/oxLDL, exhibited defective BCR signaling, and were prone to apoptosis, especially in hyperlipidemic conditions. Transfer of wild-type B1b cells in CD40BKO mice prevented the increase in atherosclerosis. Conclusions: Patients with severe CAD had similar CD40 expression levels on most B-cell subsets but showed a profound decrease in CD40 on putative B1 cells. This was associated with increased atherosclerotic plaque burden and decreased plaque fibrosis. Likewise, CD40BKO mice exhibited an increased plaque area and more advanced staging of atherosclerosis. Absence of CD40 on B-cells caused a decrease in immunoglobulin (Ig) producing cells, including germinal center-, plasma-, but especially B1 cells, thereby reducing levels of (anti-ox/MDA-LDL) IgG and protective (anti-ox/MDA-LDL) IgM. Transcriptomics analysis revealed that the absence of CD40 on B1b cells caused altered gene expression pathways related to lipid uptake (Cd36, Ldlr), cellular stress and metabolism (Nr4a1, Hif1a), and cell death (Naip5/6, Ccnd2). Indeed, in vitro analysis showed that B1bCD40KO cells took up excessive amounts of ac/oxLDL, exhibited defective BCR signaling, and were prone to apoptosis, especially in hyperlipidemic conditions. Transfer of wild-type B1b cells in CD40BKO mice prevented the increase in atherosclerosis. Comparison of gene expression in aortas (n=5 per genotype) and B1b cells (n=3 per genotype) from wild-type mice and B cell-specific CD40-deficient mice