Coinfection with Borrelia burgdorferi and the agent of human granulocytic ehrlichiosis alters murine immune responses, pathogen burden, and severity of Lyme arthritis

Lyme disease and human granulocytic ehrlichiosis (HGE) are tick-borne illne sses caused bg Borrelia burgdorferi and the agent of HGE, respectively. We investigated the influence of dual infection with B. burgdorferi and the HG E agent on the course of murine Lyme arthritis and granulocytic ehrlichiosi s. Coinfection resulted in increased le c els of both pathogens and more se vere Lyme arthritis compared with those in mice infected with B, burgdorfer i alone. The increase in bacterial burden during dual infection was associa ted with enhanced acquisition of both organisms bg larval ticks that were a llowed to engorge upon infected mice. Coinfection also resulted in diminish ed interleukin-12 (IL-I?), gamma interferon (IFN-gamma), and tumor necrosis factor alpha levers and elevated IL-6 levels in murine sera. During dual i nfection! IFN-gamma receptor expression on macrophages was also reduced, im plying a decrease in phagocyte activation. These results suggest that coinf ection of mice with B. burgdorferi and the HGE agent modulates host immune responses, resulting in increased bacterial burden, Lyme arthritis, and pat hogen transmission to the vector.