Thrombocytopenia is a frequent complication of viral infections providing evidence that interaction of platelets with viruses is an important pathophysiological phenomenon. Multiple mechanisms are involved depending on the nature of the viruses involved. These include immunological platelet destruction, inappropriate platelet activation and consumption, and impaired megakaryopoiesis. Viruses bind platelets through specific receptors and identified ligands, which lead to mutual alterations of both the platelet host and the viral aggressor. We have shown that HIV-1 viruses are internalized specifically in platelets and megakaryocytes, where they can be either sheltered, unaltered (with potential transfer of the viruses into target organs), or come in contact with platelet secretory products leading to virus destruction and facilitated platelet clearance. In this issue, we have reviewed the various pathways that platelets use in order to interact with viruses, HIV and others. This review also shows that more work is still needed to precisely identify platelet roles in viral infections, and to answer the challenge of viral safety in platelet transfusion.

Platelet dysfunction after cardiopulmonary bypass (CPB) can contribute to excessive post-operative bleeding. Most trials of the protective effect of aprotinin in this setting have involved hypothermic CPB, which is more deleterious for platelets than normothermic CPB. Here we investigated the effect of aprotinin on platelet function during normothermic CPB in pediatric patients. Twenty patients (9 newborns [<1 month old] and 11 infants [<36 month old]), weighting less than 15 kg and undergoing normothermic CPB (35-36 degrees C) were randomly assigned to two equal groups, one of which received high-dose aprotinin. Platelet function was assessed by flow cytometry just before CPB and 5 minutes after heparin neutralization. F1 + 2 fragments were measured by ELISA before and 5 minutes after CPB. Platelet activation marker expression (CD62P and activated alphaIIbbeta3) induced by ADP or TRAP was lower after CPB than before CPB, suggesting a deleterious effect of normothermic CPB on platelet function. Prothrombin fragment F1 + 2 levels increased after CPB. Aprotinin administration did not influence the level of prothrombin fragments or platelet marker expression measured in basal condition. However, after CPB, the capacity for platelet activation was higher in the aprotinin group, as shown by measuring CD62P expression after TRAP activation (p = 0.05). This study suggests that pediatric normothermic CPB causes platelet dysfunction, and that high-dose aprotinin has a protective effect.