Abstract
Fc gamma receptor IIIA (CD16/Fc gamma RIIIA) on monocytes/macrophages may play an important role in the pathogenesis of severe malarial anemia (SMA) by promoting phagocytosis of IgG-coated uninfected red cells and by allowing the production of tumor necrosis factor alpha (TNF-alpha) upon cross-linking by immune complexes (ICs). However, not much is known about the differential expression of this receptor on monocytes of children with severe malaria and uncomplicated malaria. Therefore, we investigated the expression of CD16/Fc gamma RIIIA on monocytes of children with SMA, cerebral malaria (CM), and their age-matched uncomplicated malaria controls by flow cytometry. Since CD14 low (CD14(+)) monocytes are considered more mature and macrophage-like than CD14 high (CD14(++)) monocytes, we also compared the level of expression of CD16/Fc gamma RIIIA according to the CD14 level and studied the relationship between CD16/Fc gamma RIIIA expression and intracellular TNF-alpha production upon stimulation by ICs. CD16/Fc gamma RIIIA expression was the highest overall on CD14(+) CD16(+) monocytes of children with SMA at enrollment. At convalescence, SMA children were the only ones to show a significant decline in the same parameter. In contrast, there were no significant differences among groups in the expression of CD16/Fc gamma RIIIA on CD14(++) CD16(+) monocytes. A greater percentage of CD14(+) CD16(+) monocytes produced TNF-alpha upon stimulation than any other monocyte subset, and the amount of intracellular TNF-alpha correlated positively with CD16/Fc gamma RIIIA expression. Furthermore, there was an inverse correlation between hemoglobin levels and CD16/Fc gamma RIIIA expression in children with SMA and their controls. These data suggest that monocytes of children with SMA respond differently to Plasmodium falciparum infection by overexpressing CD16/Fc gamma RIIIA as they mature, which could enhance erythrophagocytosis and TNF-alpha production.