• The application of transcriptional profiling to uncovering of the biology of the pre-erythrocytic stages of Plasmodium and the identification of protective pre-erythrocytic stage antigens

      Williams, Calvin; Azad, Abdu F. (2009)
      Malaria, caused by infection with parasites of the Plasmodium genus, remains a serious public health threat. Plasmodium sporozoites, injected into humans by mosquitoes, migrate to the liver, invade hepatocytes and transition into merozoites. Radiation-attenuated sporozoites (RAS) are incapable of forming merozoites and shown to elicit sterile protective immune responses in humans but technical reasons prevent large-scale human immunizations using RAS. T cells, elicited by sporozoites in lymph nodes draining the site of infection that target Plasmodium infected hepatocytes, mediate this immune response. Similarly, wild-type sporozoites (wtSPZ) given to mice or humans under chloroquine treatment can illicit protection from wtSPZ challenge, suggesting that wtSPZ can be immunogenic. Together these observations imply that protective Plasmodium antigens are expressed by RAS, wtSPZ, and liver stage parasites. Unfortunately, the molecular biology of the clinically silent pre-erythrocytic stages, composed of the sporozoite and liver stages, remains largely uncharacterized. Improved understanding of the biological processes required for progression through the pre-erythrocytic stages could lead to the identification of new drug and vaccine targets. The hypothesis of this project is three part: one, the biological processes important for progression through the pre-erythrocytic stage are reflected in the transcriptional profile of the constituents of the pre-erythrocytic stages; two, RAS developmental arrest is mediated by radiation induced DNA damage that results in transcriptional changes; and three, the protective pre-erythrocytic antigens are contained within a set of commonly expressed pre-erythrocytic stage genes. To test these hypothesis, transcriptional analysis of liver stage parasites, RAS, and wtSPZ was performed, resulting in the identification of 1100 genes significantly differentially expressed during the pre-erythrocytic stages, represented within this data set are many genes involved in a variety of cellular functions. Next, the microarray results present above were combined with other Plasmodium sporozoite and liver stage proteomic and transcriptional data sets to yield a list of ~4000 P. yoelii proteins, with P. falciparum homologs and evidence of pre-erythrocytic stage expression. Application of bioinformatics tools to this combined data set yielded over 3300 Plasmodium proteins potentially involved in the protective immune response observed after immunization with Plasmodium RAS.