Platelet secretory activities in acute malaria (Plasmodium falciparum) infection.

During acute Plasmodium falciparum infection in man, plasma concentrations of platelet-specific proteins, beta-thromboglobulin (beta TG) and platelet factor 4 (PF4) were significantly elevated. For beta TG, the mean concentration was 136.24 +/- 71.58 ng/ml in patients, and 50.53 +/- 25.42 ng/ml in control subjects (t = 5.3794; p = 0.0001), while for PF4 mean values were, respectively, 75.35 +/- 23.09 and 18.64 +/- 13.42 ng/ml (t = -6.0897; p less than 0.0001). Platelet LDH loss in vitro in response to stimulation with 0.5 U of thrombin was 57.0 +/- 29.5% in patient samples and 24.8 +/- 16.9% (control); the values being significantly different from each other (t = 2.888; p less than 0.025). With serotonin (5HT) uptake and release however, the values were essentially normal, in spite of marginal difference observed in the uptake value of patients compared to control. The data indicate that there was in vivo platelet activation during the infection, with the haemostatic balance titled towards hypercoagulability. There was also associated easy platelet lysis with stimulation. It is also suggested that the latter finding may be one of the mechanisms of reduced circulating platelet numbers observed in patients in the acute disease.