Activation of the host response in human plasmodium falciparum malaria: Relation of parasitemia to tumor necrosis factor/cachectin, thrombin-antithrombin III, and protein C levels

Abstract

purpose: Hemostatic alterations and elevated tumor necrosis factor/cachectin (TNFα) serum levels may contribute to the pathogenesis of organ complications in human Plasmodium falciparum malaria. Therefore, we examined whether altered protein C (PC) and thrombin-antithrombin III (TAT) plasma levels correlated with TNFα serum concentrations, parasitemia, and the clinical course of human P. falciparum malaria. patients and methods: Forty-seven patients with P. falciparum malaria were evaluated prospectively before and during antiparasitic therapy. TNFα serum levels were determined by immunoradiometric assay, PC and TAT plasma antigen by enzyme-linked immunosorbent assay, and PC and PC inhibitor-1 (PCI-1) activity levels by functional tests. Cultured endothelial cells were incubated with serum from four patients with malaria and from healthy control subjects and then assayed for procoagulant activity. Northern blot hybridization was used to detect tissue factor mRNA. results: In vivo, TNFα serum concentrations were elevated (median: 38.6 pg/mL; n =47) while plasma levels of PC (antigen 55.4%; activity 39.0%; n = 47) and PCI-1 (0.56 U/L) were decreased in almost all patients before antiparasitic treatment. At the same time, TAT concentrations were high. These alterations correlated significantly (p <0.01) both with the severity of the disease (as defined by organ impairment) and with the number of circulating parasitized erythrocytes. Low PCI-1 activity correlated with low PC activity (p <0.001) and antigen (p <0.05) levels. The plasma level of coagulation factor IX, another vitamin K-dependent protein, was not significantly changed. In vitro, incubation of endothelial cells with patient serum (severe P. falciparum malaria) increased both endothelial cell procoagulant activity and cytoplasmic tissue factor mRNA levels. conclusion: Elevated levels of TNFα and TAT, decreased plasma levels of anticoagulant PC, and the induction of procoagulant activity in endothelial cells by patient serum indicate a shift in the balance of hemostatic activity towards a precoagulant state in P. falciparum malaria. The alterations in TNFα, TAT, and PC levels may be a response to infection, since they correlate with parasitemia and are reversed during antiparasitic treatment.