beta 2 integrin modulates platelet caspase activation and life span in mice

We explored the role of CD18 (beta2 integrin) in platelet physiology, using mice genetically deficient in CD18 (CD18 -/-), or its main ligand CD54 (IC AM-1, CD54 -/-). CD18 and CD11a were evident in platelets from +/+, but not from CD18 -/- mice, as seen by immunofluorescence or Western blots. CD18 m RNA was also detectable by RT-PCR in platelets from +/+, but not from CD18 -/- mice. The life span of platelets was significantly shorter in CD18 -/- than in +/+ or CD54 -/- mice, as seen by in vivo biotinylation. When a loca l inflammation was elicited by the intra-tracheal injection of TNF, labeled platelets from +/+, but not from CD18 -/- donors, did localize in the lung . The content of Bcl-3 was about 20-fold higher in platelet from CD18 -/-,t han in those from +/+ or CD54 -/- donors, as seen on Western blots or by im munofluorescence and flow cytometry, while the amount of pro-caspase-3 was decreased. An activation of caspases in platelets from CD18 -/- was also ev idenced by protease assays. Accordingly, gelsolin, a protein cleaved by cas pase-3, showed a low-molecular-weight band in platelets from CD18 -/- but n ot from +/+ donors. These results demonstrate that the beta2 integrin, pres ent in mouse platelets, modulates caspase activation and consequently plate let life span and response to TNF.