INHIBITION OF HUMAN NEUTROPHIL APOPTOSIS BY PLATELETS

In the absence of appropriate stimuli, polymorphonuclear neutrophils r apidly undergo characteristic changes indicative of programmed cell de ath or apoptosis. We report here that neutrophils cultured in the pres ence of platelets (neutrophil:platelet ratios of 1:50, 1:25, and 1:10) show a dramatic inhibition of apoptosis compared with neutrophils cul tured alone. Similar degrees of apoptosis delay were induced by viable unstimulated platelets, fixed unstimulated platelets, or fixed activa ted (1 U/ml thrombin) platelets, Inhibition of apoptosis was associate d with prolongation of the functional lifespan of the neutrophil, as i ndicated by the higher capacity of platelet-treated neutrophils to dis play chemiluminescence responses triggered by FMLP, immune complexes, and zymosan. The mechanism responsible for the inhibition of neutrophi l apoptosis by platelets has not yet been defined. However, it seems t hat classical recognition systems such as those mediated by the intera ction between platelet P-selectin (CD62) or glycoprotein IIb/IIIa comp lex and their counter-receptors expressed by neutrophils are not invol ved.