Aims Targeting vascular inflammation represents a novel therapeutic approach to reduce complications of atherosclerosis. Neutralizing the pro-inflammatory cytokine interleukin-1β (IL-1β) using canakinumab, a monoclonal antibody, reduces the incidence of cardiovascular events in patients after myocardial infarction (MI). The biological basis for these beneficial effects remains incompletely understood. We sought to explore the mechanisms of IL-1β-targeted therapies. Methods and Results In mice with early atherosclerosis (ApoE-/- mice on a high-cholesterol diet for six weeks), we found that three weeks of NLRP3-inflammasome inhibition or anti-IL-1β treatment (using either MCC950, an NLRP3 inflammasome inhibitor which blocks production and release of active IL-1β; or a murine analog of canakinumab) dampened accumulation of leukocytes in atherosclerotic aortas, which consequently resulted in slower progression of atherosclerosis. Causally, we found that endothelial cells from atherosclerotic aortas lowered expression of leukocyte chemoattractants and adhesion molecules upon NLRP3-inflammasome inhibition, indicating that NLRP3-inflammasome- and IL-1β-targeted therapies reduced blood leukocyte recruitment to atherosclerotic aortas. In accord, adoptive transfer experiments revealed that anti-IL-1β treatment mitigated blood myeloid cell uptake to atherosclerotic aortas. We further report that anti-IL-1β treatment and NLRP3-inflammasome inhibition reduced inflammatory leukocyte supply by decreasing proliferation of bone marrow hematopoietic stem and progenitor cells, demonstrating that suppression of IL-1β and the NLRP3-inflammasome lowered production of disease-propagating leukocytes. Using bone marrow reconstitution experiments, we observed that hematopoietic cell-specific NLRP3-inflammasome activity contributed to both enhanced recruitment and increased supply of blood inflammatory leukocytes. Further experiments that queried whether anti-IL-1β treatment reduced vascular inflammation also in post-MI accelerated atherosclerosis documented the operation of convergent mechanisms (reduced supply and uptake of inflammatory leukocytes). In line with our pre-clinical findings, post-MI patients on canakinumab treatment showed reduced blood monocyte numbers. Conclusions Our murine and human data reveal that anti-IL-1β treatment and NLRP3-inflammasome inhibition dampened vascular inflammation and progression of atherosclerosis through reduced blood inflammatory leukocyte 1) supply and 2) uptake into atherosclerotic aortas providing additional mechanistic insights into links between hematopoiesis and atherogenesis, and into the beneficial effects of NLRP3-inflammasome- and IL-1β-targeted therapies. Translational perspective Therapeutic targeting of vascular inflammation represents a promising avenue to reduce complications of atherosclerosis. Neutralizing the pro-inflammatory cytokine interleukin-1β (IL-1β) reduces the incidence of cardiovascular events in patients with prior myocardial infarction. However, the mechanisms underlying these beneficial effects remain incompletely understood. This study explored how IL-1β and NLRP3-inflammasome suppression mitigated plaque progression. Our murine and human data reveal that pharmacological anti-IL-1β treatment and NLRP3-inflammasome inhibition dampened inflammatory leukocyte accumulation in atherosclerotic aortas through 1) decreased blood inflammatory leukocyte supply and 2) reduced blood inflammatory leukocyte uptake into in atherosclerotic aortas. These data provide additional mechanistic insights into links between hematopoiesis and atherogenesis, and inform future anti-inflammatory interventions in patients with atherosclerosis.

Aims Mental stress substantially contributes to the initiation and progression of human disease, including cardiovascular conditions. We aim to investigate the underlying mechanisms of these contributions since they remain largely unclear. Methods and results  Here, we show in humans and mice that leucocytes deplete rapidly from the blood after a single episode of acute mental stress. Using cell-tracking experiments in animal models of acute mental stress, we found that stress exposure leads to prompt uptake of inflammatory leucocytes from the blood to distinct tissues including heart, lung, skin, and, if present, atherosclerotic plaques. Mechanistically, we found that acute stress enhances leucocyte influx into mouse atherosclerotic plaques by modulating endothelial cells. Specifically, acute stress increases adhesion molecule expression and chemokine release through locally derived norepinephrine. Either chemical or surgical disruption of norepinephrine signalling diminished stress-induced leucocyte migration into mouse atherosclerotic plaques. Conclusion  Our data show that acute mental stress rapidly amplifies inflammatory leucocyte expansion inside mouse atherosclerotic lesions and promotes plaque vulnerability.

Atherosclerosis is the leading cause of death worldwide and leukocyte recruitment is a key element of this phenomenon, thus allowing immune cells to enter the arterial wall. There, in concert with accumulating lipids, the invading leukocytes trigger a plethora of inflammatory responses which promote the influx of additional leukocytes and lead to the continued growth of atherosclerotic plaques. The recruitment process follows a precise scheme of tethering, rolling, firm arrest, crawling and transmigration and involves multiple cellular and subcellular players. This review aims to provide a comprehensive up-to-date insight into the process of leukocyte recruitment relevant to atherosclerosis, each from the perspective of endothelial cells, monocytes and macrophages, neutrophils, T lymphocytes and platelets. In addition, therapeutic options targeting leukocyte recruitment into atherosclerotic lesions—or potentially arising from the growing body of insights into its precise mechanisms—are highlighted.