Response to Plasmodium Falciparum-Derived TLR Ligands in Severe and Uncomplicated Malaria in Mali

Malaria remains an important public health threat, responsible for over two million deaths annually, the majority among African children. The mechanisms underlying resistance to the most severe manifestations of malaria remain elusive. Severe malaria has been associated with high levels of pro-inflammatory cytokines that may contribute to the pathogenesis of cerebral malaria, severe anemia and acidosis. This response is thought to be driven primarily by glycosylphosphatidylinositol (GPI) anchors derived from erythrocyte-stage Plasmodium falciparum. It has been suggested that antibodies against GPI are responsible for resistance to severe malaria, which has led to efforts to develop a GPI-based vaccine. An alternative explanation for the development of resistance to severe malaria is down regulation of the innate pro-inflammatory response by repeated ligation of toll-like receptors (TLR) by GPI, or other putative P. falciparum-derived TLR ligands, such as hemozoin. This cross-sectional study at l'Hopital Gabriel Toure in Bamako, Mali, proposes to test the hypothesis that resistance to severe malaria is associated with an attenuation of the TLR-mediated pro-inflammatory cytokine response. After informed consent is obtained from the participant's parent or guardian, 2-3 mL of venous blood will be drawn from each of 60 children: 40 children presenting with acute P. falciparum infection (20 severe and 20 uncomplicated) and 20 healthy, P. falciparum uninfected controls. The blood will be tested for antibody titers against GPI and Merozoite Surface Protein-1 (MSP-1). Peripheral blood mononuclear cells (PBMCs) will be isolated and cultured with GPI, hemozoin, lipoteichoic acid (LTA), lipopolysaccharide (LPS), and cytosine-guanine dinucleotide (CpG). At 24 hours, supernatant will be collected and the following cytokines measured: IL-1, IL-6, IL-8, IL-10, IL-12, and TNF-alpha. A clearer understanding of the responsiveness to TLR ligands in children from malaria endemic areas may provide information on potential intervention strategies such as GPI-based vaccines or the use of TLR agonists as vaccine adjuvants.