Effects of Plasmodium Falciparum Infection on Monocyte and Neutrophil Function: A Basis for Increased Destruction of Unparasitized Erythrocytes

Abstract

It has become certain that partof the haemolytic componentof the anaemia of Plasmodium falciparum malaria results from increased removal of unparasitized red blood cells. There have been several reports of associations between positive Coombs’ DAT and anaemia, and also of observations of unparasitized erythrocytes in monocytes of patients with P. falciparum infections. Perturbations in cytokine balance have also been blamed for reduced red cell survival as well as for defective erythropoiesis. This study sought to ascertain to what extent increase in monocyte and neutrophil function and the general inflammatory response to P. falciparum infections contribute to the anaemia of malaria. Neutrophil phagocytic activity, monocytes surface expression of HLA-DR and FcγRIII, and plasma levels of IL-10, TNF-α, IL- 8, neopterin, MIP-lα and MIP-1β were compared among groups of children with sesvere P. falciparum malaria anaemia (SA), others with other forms of malaria (cerebral, CM or uncomplicated, UM) and healthy or asymptomatic controls (AC). Phagocytic activity was measured as ability of neutrophils to take up fluorescent latex particles. All groups of children with symptomatic malaria showed higher neutrophil phagocytic activity than the control group (p<0.005). Further, among the children with symptomatic malaria, children in the SA group showed a higher phagocytic activity than the others (SA vs. CM, p=0.029; SA vs. UM, p=0.002). There was a marked reduction in monocyte expression of HLA-DR in all groups of patients compared to controls (p<0.001), but differences among patient groups were not significant. Plasma levels of all cytokines measured were not significantly different in the SA group compared to other groups of patients (p>0.05), but were markedly elevated in all patient groups compared to controls (p<0.05).