Some human chemokines are stored for regulated secretion in endothelial cells but such sorting has not been described until now in the mouse.

Rapid translocation of P-selectin from WPB to the surface of endothelial cells is crucial for early neutrophil recruitment to acute inflammatory lesions. Likewise, the chemokine CXCL8/IL-8 is sorted to WPB in human endothelial cells, but little is known about its functional importance in lack of a suitable animal model. Here, we explored the distribution of the functional IL-8 homologues CXCL1/KC, CXCL2/MIP-2, and CXCL5-6/LIX in resting and inflamed murine vessels by confocal microscopy and paired immunostaining with markers of WPB, discovering that these chemokines did not localize to WPB but displayed a granular pattern in a subset of vessels in healthy skin compatible with sorting to the type 2 endothelial compartment for regulated secretion. Moreover, all chemokines colocalized with VWF and P-selectin in platelets, suggesting that their storage in platelet α-granules might represent an alternative source of rapidly available, neutrophil-recruiting chemokines. In conclusion, WPB appear not to be involved in regulated secretion of chemokines in the mouse, and instead, the possible existence of type 2 granules and the role of platelets in rapid leukocyte adhesion deserve further attention.