Analysis of the short-term effects of platelets on EVT function. (A-B) The isolated human EVTs were plated on collagen type I in the presence of PBMC-CM or platelet-CM. The viable cell number (A) and the apoptotic cell number (B) after 12 hours of culture were assessed as described in “Materials and methods.” The number of viable cells (viability) was significantly higher (A) and the number of apoptotic cells was significantly lower in the presence of PBMC-CM (B), but such effects were not observed with platelet-CM. (C-D) Matrigel invasion of isolated human EVTs toward platelet-CM with or without heat treatment or charcoal stripping in the presence or absence of anti-CCD1 mAb was assessed as described in “Materials and methods.” The invasion-promoting effect of platelet-CM on isolated EVTs was completely abrogated by heat treatment but not changed by charcoal stripping (C). Preincubation of isolated EVTs with the anti-CCR1 antibody significantly reduced the invasion-promoting effect of platelet-CM (D). *P < .05; **P < .01; NS, not significant.