The proposed project is to identify the molecular basis of the antigens involved in tick immunity and study its effects upon the transmission of Lyme borreliosis and Ehrlichiosis. Specifically a model of tick protective immunity has been established in guinea pigs. Antibodies already shown to be capable of passively protecting recipients will be purified using chemical and immunoabsorbent methods. Tick salivary antigens will be obtained for Ixodes scapularis; these antigens will be purified by chemical and immunological means using the purified protective antibodies described above. Such antigens will be used to actively produce tick immunity in the model. With purified antibodies obtained from tick-sensitized animals, cDNA libraries already prepared from salivary glands will be screened. Such libraries, prepared from stimulated tick salivary glands, will be used to clone genes encoding protective antigens. Several putative clones have already been identified. Recombinant antigens will be expressed, purified, and characterized before use as immunogens to immunize rice and guinea pigs to determine their potential for induction of anti-tick immunity. Using immune guinea pigs, the effect of anti-tick immunity on the ability of ticks infected with either Borrelia burgdorferi or Ehrlichia canis to transmit disease to tick-immune hosts will be determined. The kinetics of transmission from infecting tick to guinea pig host will be the basis of studies on the mechanism of how anti-tick immunity affects pathogen transmission.