Impaired adhesion of neutrophils expressing Slc44a2/HNA-3b to VWF protects against NETosis under venous shear rate.

Abstract Genome wide association studies linked expression of the human neutrophil antigen 3b (HNA-3b) epitope on the Slc44a2 protein with a 30% decreased risk of venous thrombosis (VT) in humans. Slc44a2 is a ubiquitous transmembrane protein identified as a receptor for Von Willebrand factor (VWF). To explain the link between Slc44a2 and VT we wanted to determine how Slc44a2 expressing either HNA-3a or HNA-3b on neutrophils could modulate their adhesion and activation on VWF under flow. Transfected HEK293T cells or neutrophils homozygous for the HNA-3a- or the HNA-3b-coding allele were purified from healthy donors and perfused in flow chambers coated with VWF at venous shear rates (100s−1). HNA-3a expression was required for Slc44a2-mediated neutrophil adhesion to VWF at 100s−1. This adhesion could occur independently of β2 integrin and was enhanced when neutrophils are preactivated with lipopolysaccharide (LPS). Moreover, specific shear conditions with high neutrophil concentration could act as a “second hit”, inducing the formation of neutrophil extracellular traps. Neutrophil mobilization was also measured by intravital microscopy in venules from SLC44A2-knockout and wild-type mice after histamine-induced endothelial degranulation. Mice lacking Slc44a2 showed a massive reduction in neutrophil recruitment in inflamed mesenteric venules. Our results show that Slc44a2/HNA-3a is important for the adhesion and activation of neutrophils in veins under inflammation and when submitted to specific shears. Neutrophils expressing Slc44a2/HNA-3b not being associated with these observations, these results could thus explain the association between HNA-3b and a reduced risk for VT in humans.