Date of Award

12-10-1988

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Microbiology & Immunology

Abstract

Ticks are both vectors and reservoirs for significant pathogens of man and livestock. They are currently controlled through use of acaracides, but have rapidly developed resistance to every new acaracide produced to date. Alternative methods of control are needed. One proposed alternative is immunologic control, achieved through vaccinations which induce resistance to tick infestation. This proposal stems from the knowledge that cattle and laboratory animals actively acquire resistance to infestation. Immunization with crude extracts of different ixodid life cycle stages or organs has induced limited levels of resistance compared to acquired resistance. Defined tick antigens are needed to study the immunopathology and to develop vaccines.Dermacentor andersoni salivary gland antigen (SGA) and ova extract, and Amblyomma americanum ova extract and gut antigens were fractionated by sodium dodecyl sulfate polyacrylamide gel electrophoresis and electroeluted to nitrocellulose for immunoblotting. Antibodies from resistant guinea pigs and rabbits were used for immunodetection of immunogenic components in these fractionated tick extracts. Ultrafiltration and Sephadex gel filtration chromatography were used to fractionate A. americanum whoel ova extract into defined molecular weight range fractions. These fractions were used in skin testing and immunization trials.Skin testing elicited both immediate and delayed hypersensitivity reactions. Immunization with ultrafiltration 30-100 Kdal fraction and its gel filtration counter part based on SDS-PAGE molecular weight determination, peak 2, induced resistance in tick naive guinea pigs to larval A. americanum infestation, comparable to acquired resistance. A component of gut antigen, 27,000 x g supernatant, induced a statistically significant level of resistance, in guinea pigs, to adult A. americanum. This resistance differs from acquired resistance in that the immunopathology occurs inside the tick and not in the skin of the host.Hybridoma cell lines which produce monoclonal antibodies to D. andersoni ova extract and SGA were developed. Immunologic cross reactivity between A. americanum and D. andersoni was illustrated by immunoblotting, and cross resistance was demonstrated through sequential infestations. Cross reactive epitopes are candidate molecules to include in a vaccine because they will potentially broaden the coverage to multiple ixodid genera. Immunologic control of ticks is a realistic and achievable goal.

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