The Vector Molecular Biology Unit focuses on the molecular aspects of arthropod vector salivary and midgut proteins in vector/host and vector/parasite interactions. The two main hypotheses driving the research of this unit are: 1) Cellular immune responses to vector arthropod salivary proteins produce an inhospitable environment in the skin of the host to the co injected pathogen, resulting in indirect killing or unsuccessful establishment in the vertebrate host. Identifying the vector salivary proteins producing cellular immune responses will help us to understand the immunologic basis of protection and to select vaccine candidates to prevent pathogen transmission. 2) A specific receptor in the sand fly midgut is required for Leishmania attachment; this interaction is necessary for survival and development of the parasite to the infective stage in the insect vector. Characterization of the midgut receptor will help in the understanding of the molecular basis of Leishmania sand fly interactions and may identify a suitable target for a transmission blocking vaccine. The efforts of the Unit are directed toward developing functional genomic approaches based on high throughput DNA vaccine construction, DNA immunization strategies, reverse antigen screening, immunologicl assays, and biochemical approaches to characterizing the interactions between vector and mammalian host and vectors and the parasite they carry. Additionally, these vector proteins may represent potential vaccine candidates to control vector borne diseases. The unit has successfully developed a functional genomic approach to identify vector salivary proteins from different sand flies that can produce antibody and or cellular immune responses which may be detrimental for pathogen or parasite establishment. The approach is based in the selection of transcripts coding for secreted proteins from a sand fly salivary gland cDNA library, cloning of these molecules into a high-throughput DNA vaccine plasmid, and intradermal immunization of these DNA plasmids in animals to test for production of immune responses. With this approach we identified vector salivary proteins capable to produce a delayed skin response (DSR), a surrogate of cellular immune response. With this approach we identified sand fly salivary DNA plasmids that can produce DSR and prevent cutaneous leishmaniasis in mice. The unit has identified the sand fly midgut receptor for the Leishmania parasite. This receptor is essential for Leishmania parasite survival and development in the gut of the fly. The practical use of this knowledge is the development of transmission blocking vaccines which target vector midgut proteins and interrupt the attachment of the parasite to the sand fly midgut hence preventing development of the parasite in the insect gut. The receptor is a galactose binding protein (named PpGalec); it is highly expressed on the surface of the midgut epithelium on the sand fly and is used for the attachment site for Leishmania major by the binding of the galactose residues on the lipophosphoglycan outersurface structure of the parasite. When sand flies were fed on blood containing parasites and antibodies against PpGalec, the number of parasites present in the gut of the fly at day 14 decreased by more than 80% and the number of infective forms decreased by 89%. These findings demonstrate that vector midgut proteins are potential targets for transmission blocking vaccines.
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