Final Report Summary - MALMASQ (Understanding immune evasion by malaria parasites) Malaria remains one of the deadliest infectious diseases affecting human kind today. The majority of its victims are young children and pregnant woman. While several parasite species may cause malaria, the deadliest form of human malaria is caused by Plasmodium falciparum. These parasites are transmitted to human by anopheles’ mosquitos and cause diseases when they reach the blood stream, invade human red blood cells and begin proliferating. The virulence of P. falciparum is attributed to its ability to change the infected red blood cells by placing its own proteins on the surface of the red cells, which in return become “sticky” and may block the circulation in small blood vessels in deep tissue which may cause sever tissue damage. By making the infected red blood cell sticky the parasite ensures that it is not removed by the spleen, which is one way by which these parasites avoid the immune system. However, placing its proteins on the surface of the red cell the parasite expose itself to immune attack mediated by human antibodies against these surface proteins. To evade this antibody mediated response the parasite had evolved a fascinating way to switch between expression of different variants of these surface antigens, while ensuring that only one is expressed at a time to avoid unnecessary exposure to the immune system. Thus, the ability of the parasite to evade immunity depends largely on expression of only a single variant at a time on the surface of the red blood cell and on its ability to switch expression between the genes encoding for these variable antigens. In an attempt to shed light on how the var gene family, which is responsible for this phenomenon is operated, our project focused on the regulatory elements found in each member of the gene family in attempts to understand how a single gene is chosen for activation while the rest of the gene family remains silent. We identified DNA sequence elements which were shown to be essential for silencing and exclusive expression of these antigens. We found that these sequences bind specific nuclear proteins which we suspected might play a role as regulators and characterized several of these proteins. We identified a couple of proteins that bind these sequences at specific places on the chromosomes, which appear to play a role in regulating structural conformation of the chromosome that may influence gene expression. In addition to DNA elements we identified a RNA molecule which does not encode for a protein but instead has a regulatory role in the “choice” of the var gene that is going to be activated. In addition to its role in activating a single var gene we found that these molecules may “mark” a specific gene and be involved in recruitment of proteins that contribute to the proper activation of the gene which was chosen. We further found that these RNA molecules associate with nuclear metabolic enzymes essential for proper gene activation at specific nuclear sub-compartment. As expected from such scientific project not all of our hypotheses were proven, however, our non-biased experimental approach led us to several unexpected new avenues of research. We identified a novel function for a small proteins in regulating the pathogenicity of pregnancy associated malaria which is one the severe manifestations of human malaria. We found surprising moonlighting role of an RNA-binding protein in protecting the genome integrity of the parasite. In addition, we found that neutrophils - which are the most abundant immune cells in the blood stream confers a strong selective pressure against a subset of variable surface antigens which were implicated in cerebral malaria.
