Monocyte activation and cytokine production in Malawian children presenting with P. falciparum malaria

Abstract

Malaria in malaria-naïve adults is associated with an inflammatory response characterized by expression of specific activation markers on innate immune cells. Here, we investigate activation and adhesion marker expression, and cytokine production in monocytes from children presenting with cerebral malaria (CM, n = 36), severe malarial anaemia (SMA, n = 42) or uncomplicated malaria (UM, n = 66), and healthy aparasitemic children (n = 52) in Blantyre, Malawi. In all malaria groups, but particularly in the two severe malaria groups, monocyte expression of CD11b, CD11c, CD18, HLA-DR and CD86, and percentages of TNF-α- and IL-6-producing monocytes were lower than in healthy controls, while expression of CD11a, TLR2 and TLR4 was lower in children with severe malaria compared with controls. These levels mostly normalized during convalescence, but percentages of cytokine-producing monocytes remained suppressed in children with SMA. In all malaria groups, especially the SMA group, a greater proportion of monocytes were loaded with haemozoin than among controls. In a P. falciparum hyperendemic area, monocytes in children with acute symptomatic malaria have reduced expression of adhesion molecules and activation markers and reduced inflammatory cytokine production. This immune suppression could be due to accumulation of haemozoin and/or previous exposure to P. falciparum.

Keywords: integrins; monocytes; toll-like receptors and cytokines.

Figure 1

Gating strategy for determining the monocyte population in the side‐scatter/CD14 plot (a) the proportion of TNF‐alpha‐producing (b) and IL‐6‐producing (c) monocytes.

Figure 2

(a to h): Medians (10th and 90th percentiles) of geometric mean florescence intensity (GMFI) of CD11a (a), CD11b (b), CD11c (c), CD18 (d), TLR‐2 (e), TLR‐4 (f), HLA‐DR (g) and CD86 (h) expressions on monocytes from children presenting with UCM, SMA and CM, compared to monocytes from healthy aparasitaemic children. ***P < 0·0001, **P < 0·001, *P < 0·05.

Figure 3

(a to h): Medians (10th and 90th percentiles) of geometric mean florescence intensity (GMFI) of CD11a (a), CD11b (b), CD11c (c), CD18 (d), TLR‐2 (e), TLR‐4 (f), HLA‐DR (g) and CD86 (h) expression on monocytes in children acute malaria (UCM, SMA and CM) and at follow‐up during convalescence (UCM‐F, SMA‐F and CM‐F), compared with monocytes from healthy aparasitaemic children. ***P < 0·0001, **P < 0·001, *P < 0·05.

Figure 4

Gating strategy for determining the monocyte population in the side‐scatter/CD14 plot (a), the geometric mean fluorescent intensity (GMFI) values for monocyte surface markers CD11a (b), CD11b (c), CD11c (d), CD18 (e), activation marker HLR‐DR (f), Toll‐like receptor 2 (g), activation marker CD86 (h) and TLR‐4 (i) expressed on monocytes. The grey histograms represent the GMFI of the isotype controls, and the white histogram represents the GMFI of the different surface and activation markers.

Figure 5

(a to b): Medians (10th and 90th percentiles) of percentage of TNF‐α‐ (a) and IL‐6‐producing monocytes (b) in children presenting with acute disease (UCM, SMA and CM) and at follow‐up during convalescence (UCM‐F, SMA‐F and CM‐F), compared with monocytes from healthy aparasitaemic children. ***<0·0001, **P < 0·001, *P < 0·05.