Our findings unveil a new mechanism by which the pericardial AT coordinates immune cell activation, granulopoiesis, and outcome after MI.

CXCR4 identifies an immobilized BM precursor (i.e., transitional premonocyte [TpMo]) that proliferates and replenishes mature Ly6Chi monocytes in mice and humans. Upon entering the circulation, CXCR4 governs monocyte margination in the lung vasculature.

No abstract

Healthy individuals of African ancestry have neutropenia that has been linked with the variant rs2814778(G) of the gene encoding atypical chemokine receptor 1 (ACKR1). This polymorphism selectively abolishes the erythroid cell expression of ACKR1, causing Duffy-negative phenotype. Here we describe an unexpected fundamental role that ACKR1 plays in hematopoiesis and provide the mechanism linking its absence with neutropenia. Nucleated erythroid cells highly expressed ACKR1, which facilitated their direct contacts with the hematopoietic stem cells. The absence of erythroid ACKR1 altered murine hematopoiesis, including stem and progenitor cells, ultimately giving rise to phenotypically distinct neutrophils, which readily left the circulation, causing neutropenia. Duffy-negative individuals developed a distinct profile of neutrophil effector molecules closely reflecting that in the ACKR1-deficient mice. Thus, alternative physiological patterns of hematopoiesis and bone marrow cell outputs depend on the expression of ACKR1 in the erythroid lineage providing major implications for the selection advantages that have resulted in the paramount fixation of the rs2814778(G) polymorphism in Africa.

BackgroundGlycoprotein VI (GPVI) is the essential platelet collagen receptor in atherothrombosis, but its inhibition causes only a mild bleeding tendency. Thus, targeting this receptor has selective antithrombotic potential.ObjectivesThis study sought to compare compounds interfering with platelet GPVI–atherosclerotic plaque interaction to improve current antiatherothrombotic therapy.MethodsHuman atherosclerotic plaque–induced platelet aggregation was measured in anticoagulated blood under static and arterial flow conditions (550/s, 1,100/s, and 1,500/s). Inhibition by dimeric GPVI fragment crystallizable region of IgG (Fc) masking GPVI binding sites on collagen was compared with that of 3 anti-GPVI antibodies: BLO8-1, a human domain antibody; 5C4, a fragment antigen-binding (Fab fragment) of monoclonal rat immunoglobulin G; and m-Fab-F, a human recombinant sFab against GPVI dimers.ResultsGPVI-Fc reduced plaque-triggered platelet aggregation in static blood by 51%, BLO8-1 by 88%, and 5C4 by 93%. Under arterial flow conditions, BLO8-1 and 5C4 almost completely inhibited platelet aggregation while preserving platelet adhesion on plaque. Inhibition by GPVI-Fc, even at high concentrations, was less marked but increased with shear rate. Advanced optical imaging revealed rapid persistent GPVI-Fc binding to collagen under low and high shear flow, upstream and downstream of plaque fragments. At low shear particularly, platelets adhered in plaque flow niches to GPVI-Fc–free segments of collagen fibers and recruited other platelets onto aggregates via ADP and TxA2 release.ConclusionsAnti-GPVI antibodies inhibit atherosclerotic plaque-induced platelet aggregation under static and flow conditions more effectively than GPVI-Fc. However, potent platelet inhibition by GPVI-Fc at a higher shear rate (1,500/s) suggests localized antithrombotic efficacy at denuded or fissured stenotic high-risk lesions without systemic bleeding. The compound-specific differences have relevance for clinical trials targeting GPVI-collagen interaction combined with established antiplatelet therapies in patients with spontaneous plaque rupture or intervention-associated plaque injury.