Lyme borreliosis: host responses to Borrelia burgdorferi.

The chronic inflammatory condition that develops after infection by B. burgdorferi is a complex process resulting from host responses to a limited number of organisms. Amplification mechanisms driven by potent proinflammatory molecules, i.e., IL-1, may explain the vigorous response to a paucity of organisms. Spirochete dissemination to distant locations involves adherence to and penetration across endothelium and may be facilitated by host responses that increase vessel permeability. The apparent lack of tissue tropism in Lyme disease is reflected in the organism's ability to adhere to different eucaryotic cell types in vitro and the wide distribution of B. burgdorferi in various organs of infected humans and experimentally infected animals. While phagocytosis and complement activation have been observed in vitro, the specific immune response that develops in humans is inefficient in eradicating the organisms, which may possess some mechanism(s) to evade this response. There is significant evidence for host autoreactivity based on antigenic cross-reactivity between the 41-kDa flagellar subunit and stress proteins of the spirochetes and endogenous host cell components. Although the outer surface proteins appear to be suitable candidates as targets for vaccination in animal studies, fundamental differences in the immune response to spirochetal components may preclude their use in humans.