Malaria caused by Plasmodium falciparum is one of the most important infectious diseases of humankind. Each year there is an estimated 300-660 million episodes of clinical P. falciparum malaria and 1-2 million will die from the infection. In P. falciparum, the family of var genes encode erythrocyte membrane proteins (PfEMPI), which act as virulence factors responsible for both antigenic variation and binding of infected erythrocytes to endothelium. Each parasite genome encodes approximately 60 PfEMPI proteins that differ between parasite strains and bind different host receptors. Severe malaria occurs when infected erythrocytes sequester in brain or placenta. The specific hypothesis behind the proposed research is that particular adhesive types may predispose to severe malaria because of their binding tropism. This study will determine the binding properties of PfEMPI proteins and how they affect infected erythrocyte selectivity for different microvascular endothelial cells. PfEMPI binding will be studied from a well characterized parasite isolate that has been adapted to grow in the laboratory. Parasite lines expressing specific PfEMPI variants will be generated by limited dilution cloning or by selection on different host receptors. Real-time PCR approaches with gene-specific primers to the family of var genes will be used to define the var genes expressed in the various lines. The specific adhesion properties of each PfEMPI protein will be determined by characterizing infected erythrocyte adhesion against an extensive panel of host receptors and microvascular endothelial cells. These studies will contribute to a detailed characterization of the cytoadhesive properties of a parasite and enable a greater understanding of the molecular basis of malaria pathogenesis.