Abstract 1044: Entpdase1 (CD39) Downregulates Monocyte And Neutrophil MAC-1 Expression
The ecto-enzyme ENTPDase1 (CD39) has been shown to limit neutrophil and monocyte influx following brain, gut, and kidney ischemia-reperfusion injury, yet the exact mechanism remains unclear. Although it has been proposed this increased leukocyte-recruitment may be related to an effect of endothelial CD39 on endothelial barrier function, here we sought to explore a different hypothesis, one of intrinsic regulation of leukocyte trafficking by CD39 bound to the surface of the leukocytes themselves. Flow cytometry was used to analyze whole blood for adhesion molecule expression and all values were expressed relative to wild-type (WT) or vehicle injected controls. A specific upregulation of the purine responsive adhesion molecule CD11b (the μM subunit of MAC-1) was seen in CD39−/− monocytes, compared to WT controls (1.83± .25, n=6, p<0.01). The neutrophil population, conversely, did not display differences in cell surface MAC-1 at baseline (0.94 ± .14, n=6, p>0.05). However, following stimulation with the bacterial mimetic peptide fMLP, CD39−/− neutrophils showed a 34% greater increase in expression of MAC-1 compared to fMLP treated WT neutrophils (2.58 ± 0.50 vs. 1.92 ± 0.13, n=6, p<0.03). This elevated CD11b expression on fMLP stimulated CD39−/− neutrophils was highly reproducible. There was no change in CD11b expression following fMLP stimulation in WT or CD39−/− monocytes. Treatment of CD39−/− animals with a soluble apyrase (a functional analogue of CD39 which has been shown to mitigate platelet desensitization in CD39−/− mice) resulted in restoration of a near wild-type expression of CD11b on monocytes relative to vehicle injected wild-type animals (1.1 ± 0.2, p>0.05). By comparison, treatment of a wild-type animals with apyrase resulted in a 50% reduction in monocyte surface CD11b expression relative to vehicle (0.45 ± 0.03, p<0.01). These findings reveal a mechanism of leukocyte autoregulation whereby CD39 modulates leukocyte trafficking to sites of vascular injury through a mechanism of intrinsic leukocyte catabolism of nucleotides and possibly via intrinsic and localized generation of adenosine.