Slc44a2 expressed by neutrophils is important for their adhesion to VWF-A1 domain and can mediate NETosis on VWF at venous shear.
Slc44a2 importance in neutrophil recruitment on VWF is exacerbated during inflammation both in vitro and in vivo
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.