Insights into deregulated TNF and IL-10 production in malaria: implications for understanding severe malarial anaemia
1 Institut Pasteur, Unité d’Immunologie Moléculaire des Parasites URA CNRS 2581, Paris, France
2 Immunology Department, Noguchi Memorial Institute for Medical Research, College of Health Sciences, University of Ghana, Accra, Ghana
3 Department of Hematology, School of Allied Health Sciences, College of Health Sciences, University of Ghana, Accra, Ghana
4 Department of Child Health, University of Ghana Medical School, College of Health Sciences, University of Ghana, Legon, Accra, Ghana
5 Centre for Medical Parasitology, Copenhagen University Hospital (Rigshospitalet), Copenhagen, Denmark
6 Department of Clinical Microbiology, Copenhagen University Hospital (Rigshospitalet), Copenhagen, Denmark
7 Department of Infectious Diseases, Copenhagen University Hospital (Rigshospitalet), Copenhagen, Denmark
8 Department of International Health, Immunology, and Microbiology (ISIM), University of Copenhagen, Copenhagen, Denmark
9 UMR CNRS 5164, Bordeaux, France
10 Université de Bordeaux, Bordeaux, France
Malaria Journal 2012, 11:253 doi:10.1186/1475-2875-11-253Published: 1 August 2012
Severe malarial anaemia (SMA) is a major life-threatening complication of paediatric malaria. Protracted production of pro-inflammatory cytokines promoting erythrophagocytosis and depressing erythropoiesis is thought to play an important role in SMA, which is characterized by a high TNF/IL-10 ratio. Whether this TNF/IL-10 imbalance results from an intrinsic incapacity of SMA patients to produce IL-10 or from an IL-10 unresponsiveness to infection is unknown. Monocytes and T cells are recognized as the main sources of TNF and IL-10 in vivo, but little is known about the activation status of those cells in SMA patients.
The IL-10 and TNF production capacity and the activation phenotype of monocytes and T cells were compared in samples collected from 332 Ghanaian children with non-overlapping SMA (n = 108), cerebral malaria (CM) (n = 144) or uncomplicated malaria (UM) (n = 80) syndromes. Activation status of monocytes and T cells was ascertained by measuring HLA-DR+ and/or CD69+ surface expression by flow cytometry. The TNF and IL-10 production was assessed in a whole-blood assay after or not stimulation with lipopolysaccharide (LPS) or phytohaemaglutinin (PHA) used as surrogate of unspecific monocyte and T cell stimulant. The number of circulating pigmented monocytes was also determined.
Monocytes and T cells from SMA and CM patients showed similar activation profiles with a comparable decreased HLA-DR expression on monocytes and increased frequency of CD69+ and HLA-DR+ T cells. In contrast, the acute-phase IL-10 production was markedly decreased in SMA compared to CM (P = .003) and UM (P = .004). Although in SMA the IL-10 response to LPS-stimulation was larger in amplitude than in CM (P = .0082), the absolute levels of IL-10 reached were lower (P = .013). Both the amplitude and levels of TNF produced in response to LPS-stimulation were larger in SMA than CM (P = .019). In response to PHA-stimulation, absolute levels of IL-10 produced in SMA were lower than in CM (P = .005) contrasting with TNF levels, which were higher (P = .001).
These data reveal that SMA patients have the potential to mount efficient IL-10 responses and that the TNF/IL-10 imbalance may reflect a specific monocyte and T cell programming/polarization pattern in response to infection.