Increased Adhesive Potential of Antiphospholipid Syndrome Neutrophils Mediated by β2 Integrin Mac‐1

Abstract

Objective While the role of antiphospholipid antibodies in activating endothelial cells has been extensively studied, the impact of these antibodies on the adhesive potential of leukocytes has received less attention. This study was undertaken to investigate the extent to which antiphospholipid syndrome (APS) neutrophils adhere to resting endothelial cells under physiologic flow conditions and the surface molecules required for that adhesion. Methods Patients with primary APS (n = 43), patients with a history of venous thrombosis but negative test results for antiphospholipid antibodies (n = 11), and healthy controls (n = 38) were studied. Cells were introduced into a flow chamber and perfused across resting human umbilical vein endothelial cells (HUVECs). Surface adhesion molecules were quantified by flow cytometry. Neutrophil extracellular trap release (NETosis) was assessed in neutrophil‐HUVEC cocultures. Results Upon perfusion of anticoagulated blood through the flow chamber, APS neutrophils demonstrated increased adhesion as compared to control neutrophils under conditions representative of either venous (n = 8; P < 0.05) or arterial (n = 15; P < 0.0001) flow. At the same time, APS neutrophils were characterized by up‐regulation of CD64, CEACAM1, β2‐glycoprotein I, and activated Mac‐1 on their surface (n = 12–18; P < 0.05 for all markers). Exposing control neutrophils to APS plasma or APS IgG resulted in increased neutrophil adhesion (n = 10–11; P < 0.0001) and surface marker up‐regulation as compared to controls. A monoclonal antibody specific for activated Mac‐1 reduced the adhesion of APS neutrophils in the flow‐chamber assay (P < 0.01). The same monoclonal antibody reduced NETosis in neutrophil–HUVEC cocultures (P < 0.01). Conclusion APS neutrophils demonstrate increased adhesive potential, which is dependent upon the activated form of Mac‐1. In patients, this could lower the threshold for neutrophil–endothelium interactions, NETosis, and possibly thrombotic events.

Prothrombotic autoantibodies in serum from patients hospitalized with COVID-19

“…Neutrophils from patients with antiphospholipid syndrome also appear to have increased adhesive potential, which is dependent upon the activated form of integrin Mac-1. This pro-adhesive phenotype amplifies neutrophil-endothelium interactions, potentiates NET formation, and potentially lowers the threshold for thrombosis (63). Therapies that target NET formation have the potential to treat thrombotic diseases.…”

The interplay between neutrophils, complement, and microthrombi in COVID-19

“…Prior to COVID-19, circulating NET remnants were already known to track closely with the activity of various TMAs, including thrombotic thrombocytopenic purpura [ 77 , 78 ], hemolytic uremic syndrome [ 79 , 80 ], transplant-associated TMA [ 78 , 81 ], and likely catastrophic antiphospholipid syndrome [ 82 ]. At the same time, these TMAs are also clearly complementopathies as evidenced by the utility of inhibitors of C5 cleavage as effective therapies [ 83 ].…”

Neutrophils—Important Communicators in Systemic Lupus Erythematosus and Antiphospholipid Syndrome

“…In SLE, neutrophils display an activated phenotype with increased aggregation and platelet-neutrophil complex formation compared to neutrophils of healthy controls, and SLE neutrophils are more prone to undergo apoptosis (33–36). Increased neutrophil activation is also seen in APS, and neutrophils from APS patients have an increased expression of cell adhesion genes and proteins resulting in increased neutrophil adhesiveness (37, 38). In models of fetal injury, aPLs generates complement protein C5a via the classical pathway, and C5a is a potent chemotactic factor and activator of neutrophils.…”