PF4 and acute lung injury: Platelet secretion of several soluble mediators affects neutrophil functions under steady-state conditions and inflammation alike: Platelet-derived heterodimers consisting of platelet factor 4 (PF4) and CCL5/RANTES (regulated on activation, normal T cell expressed and secreted) stored in alpha granules (2, 25) promote neutrophil extravasation in acute lung injury (26) and are known to modulate neutrophil function in sterile inflammation (27).