Malaria during pregnancy and childhood : A focus on soluble mediators and neutrophils

Abstract: In areas where malaria is endemic, pregnant women and children bear the main burden of severe and life-threatening malarial disease. The aim of this work was to study the impact of Plasmodium falciparum infection on inflammatory responses in pregnant women and children residing in African countries. In paper I we investigated peripheral blood samples from pregnant women, living in Tanzania, for potential biomarkers of P. falciparum infection during pregnancy. We found that IL-10 and IP-10 were potential candidates, which increased upon infection, irrespective of gestational age. In addition, increased IL-10 and IP-10 and decreased RANTES levels were predictive of an infection. In paper II we investigated frequencies of peripheral blood-cell types and biomarkers upon infection, in pregnant women living in Benin, and assessed the predictive values of variables measured at inclusion for pregnancy outcomes at delivery. Higher IL-10 levels distinguished quantitative PCR-detectable, sub-microscopic infections, at inclusion, but not at delivery. Maternal anaemia at delivery was associated with increased numbers of circulating monocytes, Treg cells and IL-10 levels measured at inclusion. In paper III we investigated neutrophil functions in the context of pregnancy malaria in vivo and in vitro. Numbers of circulating neutrophils and IL-8 levels were reduced in the infected women, whilst increased levels of IL-8 were found in placental blood of those infected. In vitro assays suggested migration of neutrophils to infected placentas, which also was supported by histological examinations showing the presence of neutrophils containing hemozoin (Hz), in the infected placenta. Stimulation of neutrophils with various Hz preparations revealed distinct patterns of neutrophil activation. In paper IV we investigated cytokines and malaria-specific antibody titres in children belonging to two African ethnic groups, living in Mali, with known different susceptibility to malaria. The Fulani showed increased cytokines (IL-6, IL-8, IL-12, IFN-α, IFN-γ) and higher titres of malaria-specific antibody subclasses (IgG, IgM and IgG1-IgG3), compared to the Dogon. Taken together, this thesis shows that host biomarkers in peripheral blood may represent useful diagnostic markers for malaria during pregnancy. The neutrophil population was shown to be highly affected by the presence of P. falciparum parasites, suggesting a role for neutrophils during malaria infections. The Fulani, showed increased pro-inflammatory and antibody responses against P. falciparum parasites, as compared to Dogon, and these differences are established already at an early age.