The levels of CD16/Fc gamma receptor IIIA on CD14+ CD16+ monocytes are higher in children with severe Plasmodium falciparum anemia than in children with cerebral or uncomplicated malaria

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.

FIG. 1.

Identification and analysis of monocyte subpopulations. (A) Monocytes were identified and gated based on CD14 staining and side-scatter characteristics. (B) Gated monocytes were subdivided into monocyte subpopulations on the basis of CD14 and CD16 staining characteristics. Subpopulations are defined as CD14⁺ CD16⁺ (quadrant 1), CD14⁺⁺ CD16⁺ (quadrant 2), CD14⁺⁺ CD16⁻ (quadrant 3), and CD14⁺ CD16⁻ (quadrant 4).

FIG. 2.

The expression of CD16/FcγRIIIA on total CD16⁺ monocytes (A) or the CD14⁺ CD16⁺ (B) or CD14⁺⁺ CD16⁺ (C) monocyte subpopulation from children within the SMA and CM cohorts at enrollment (visit 1) and follow-up visits (visit 2).

FIG. 3.

Intracellular TNF-α production by different monocyte subpopulations stimulated with IC compared to that of unstimulated, IgG and LPS-treated controls. Results are expressed as mean values ± standard deviations of percentages of monocytes from 24 children (SMA group [n = 9], SMA controls [n = 10], and CM controls [n = 5]) that produced TNF-α. CD14⁺ CD16⁺ monocytes had the highest percentage of TNF-α-positive cells, followed by the CD14⁺⁺ CD16⁺ subset. TNF-α expression by CD14⁺ CD16⁻ and CD14⁺⁺ CD16⁻ monocytes in response to IC stimulation was negligible.

FIG. 4.

Correlation between CD16/FcγRIIIA expression levels on CD14⁺ CD16⁺ (A) and CD14⁺⁺ CD16⁺ (B) monocyte subpopulations with TNF-α production levels in response to IC stimulation.

FIG. 5.

Correlation between hemoglobin and CD16/FcγRIIIA expression levels on total CD16⁺ monocytes (A) or the CD14⁺ CD16⁺ (B) or CD14⁺⁺ CD16⁺ (C) monocyte subpopulation from SMA cases and controls.