Characterization of a filarial retinol-binding protein

Date of Completion

January 1996


Health Sciences, Pathology|Health Sciences, Immunology




Filarial parasites are a major public health problem in a number of third world countries, where there are an estimated 120,000,000 cases of lymphatic filariasis and 20,000,000 cases of onchocerciasis. In an attempt to generate a recombinant DNA based subunit vaccine for this disease, our laboratory has focused on aspects of the parasite's metabolism that are unique to it and distinct from that of the host. One function that appears to be critical in parasite physiology is the accumulation of retinoids. Considerable evidence in the literature suggests that filarial parasites sequester retinoids by synthesizing high affinity retinol binding proteins (RBP). The current work is based on the hypothesis that an immune response against parasite RBP should prevent the sequestration of retinoids by filarial parasites and thereby prevent their growth in the mammalian host. Using a combination of ion-exchange and size separation chromatography, we have purified a retinol-binding protein from the dog heartworm Dirofilaria immitis, and obtained the N-terminal amino acid sequence of the protein. The 37 amino acid sequence does not match any of the RBP's catalogued in GenBank, which are all of vertebrate origin. The sequence does, however, show almost complete identity with a sequence previously reported by Tremholme, et al, to be that of a highly immunogenic antigen derived from the human filarial parasite, Onchocerca volvulus. The published sequence of this antigen (Ov20/11) was used to synthesize oligonucleotide primers for PCR amplification and several recombinant expression clones were generated. Detailed analyses of these clones showed that the recombinant clones also exhibited retinol binding activity. This thesis describes the characterization of a filarial retinol-binding protein and discusses it's potential as a vaccine candidate in filarial disease. ^