PLATELET ACTIVATION IN NEWBORNS DETECTED BY FLOW-CYTOMETRY

Platelet function was investigated in full-term infants on the first, the fourth and the tenth days of life and compared to normal adult con trols. Platelet function was analyzed through a new cytofluorimetric t echnique with two murine monoclonal antibodies, PAC-1 and anti-GMP-140 , directed against two membrane proteins expressed on the activated pl atelets' surface. The percentage of activated platelets detected with PAC-1 and anti-GMP-140 was evaluated at basal condition and after in v itro stimulation with a wear; agonist (ADP) and a strong Txa(2) analog ue inducer (Li 46619). At day I platelet activation at basal condition was negligible and similar to adult controls both with PAC-1 (1.2 vs, 1.1%) and anti-GMP-140 (2.6 vs, 3.3%), On the contrary, after ADP sti mulation the percentage of PAC-1-positive activated platelets was sign ificantly reduced in neonates compared to adults (22 vs. 66%; p < 0.00 1) and even more after U 46619 (11 vs., 72%; p < 0.001). The percentag e of anti-GMP-140-positive activated platelets behaved similarly after adding both ADP (26 vs. 46% p < 0.01) and U 46619 (37 vs. 67%,; p < 0 .001). The reduced platelet activation after ADP and U 46619 persisted at day 4 both with PAC-1 and with anti-GMP-130. On the contrary, at d ay 10 newborn platelets analyzed with anti-GMP-140 behaved similarly t o tile adult ones both at basal condition and after stimulation with A DP or U 46619 (6 vs. 3% at basal. state, 42 vs. 46% after ADP addition , and 55 vs. 67% after U 46619). These data demonstrate that the reduc ed platelet activation present in newborns is restored by the tenth da y after birth.