Interactions between rickettsiae and Dermacentor variabilis ticks: analysis of gene expression.

Tick-borne spotted fever group rickettsiae are maintained in nature primarily through transstadial and transovarial transmission in their vector. In the tick, Dermacentor variabilis, the infection of, and persistence within, the ovaries are critical steps in the transmission cycle of rickettsiae from one generation to the next. Although ixodid ticks can experimentally maintain several species of rickettsiae, often only a single species is maintained transovarially. The molecular mechanisms underlying exclusion processes are unknown. In this study, an attempt to identify the molecules that may be involved in rickettsial adhesion to tick cells was carried out. Monoclonal antibodies to mammalian alpha and beta subunits of integrins were used to screen a lambda phage library, constructed from uninfected tick ovarian tissues. Positive plaques for both alpha and beta integrins were identified. For one integrin, beta(3), the plaque was isolated and the insert sequenced. The role of these molecules, identified by library screening, in rickettsial infection and survival are discussed.