Role of complement receptor 1 in erythrocyte invasion by Plasmodium falciparum

Objectives

This proposal aims to extend previous studies to the field to examine the role of CR1 in mediating red cell invasion in semi-immune individuals. Successful completion of these proposed studies will substantially increase our understanding of the invasion mechanisms that are used by malaria parasites in Ghana which has broad implications on the design of potential blood-stage interventions. In addition, these investigations will significantly enhance the career of the PI and contribute towards capacity-building at the University of Ghana, both in infrastructure and technology for malaria research.

This objective will be achieved through:

1. Parasite isolates collected from three geographically distinct zones of Ghana with varying transmission intensities will be examined for their erythrocyte invasion mechanisms by testing their ability to invade erythrocytes treated with neuraminidase, trypsin, or chymotrypsin, which selectively disrupt specific erythrocyte receptors.
2. In addition, the contribution of CR1 as a receptor will be investigated by measuring the ability of anti-CR1 antibodies and soluble CR1 to inhibit erythrocyte invasion. 
3. Erythrocyte CR1 expression in semi-immune individuals will also be measured by flow cytometry and the association with peripheral parasite density will be investigated. 
4. In addition, titers of antibodies against the major SA-dependent ligands including, EBA-140, EBA-175, and EBA-181, as well as the CR1 ligand Rh4, will be determined by ELISA and their impact on the relationship between CR1 and parasitemia will be examined using a multivariate statistical model. 
5. For parasite isolates whose invasion phenotypes are determined, gene expression of the known SA-independent parasite ligands Rh2a, Rh2b, and Rh4, as well as candidate ligands that will be identified in our ongoing investigations of CR1 ligands, will be determined by quantitative real-time (RT) -PCR. 
6. The relationship between erythrocyte receptor usage, anti-EBA antibody titers and ligand gene expression will then be examined to definitively show if increased anti-EBA titers are associated with an increased CR1 ligand gene expression and switch to CR1-dependent invasion phenotype.