Attachment of Borrelia burgdorferi within Ixodes scapularis mediated by outer surface protein A

Borrelia burgdorferi outer surface protein (Osp) A has been used as a Lyme disease vaccine that blocks transmission: OspA antibodies of immune hosts e nter ticks during blood feeding and destroy spirochetes before transmission to the host can occur. B. burgdorferi produce OspA in the gut of unfed Ixo des scapularis ticks, and many spirochetes repress OspA production during t he feeding process. This preferential expression suggests that OspA may hav e an important function in the vector. Here we show that OspA mediates spir ochete attachment to the tick gut by binding to an I. scapularis protein. T he binding domains reside in the central region and COOH-terminus of OspA. OspA also binds to itself, suggesting that spirochete-spirochete interactio ns may further facilitate adherence in the gut. OspA-mediated attachment in the tick provides a possible mechanism for how stage-specific protein expr ession can contribute to pathogenesis during the B. burgdorferi natural cyc le.