| Lyme disease, the most prevalent vector-borne disease in the United States, is caused by the spirochete Borrelia burgdorferi (Bb). After transmission via tick-bite, Bb remains within the skin for 12 to 48 hours before disseminating to numerous tissues. While Bb lacks several stimulatory cellular components typical of Gram-positive and Gram-negative bacteria, it produces many lipoproteins that potently elicit inflammatory responses via Toll-like receptor-2 (TLR2). Although TLR2-mediated responses are critical for controlling Bb numbers, the responding cells often fail to clear the infection, allowing the bacteria to disseminate and establish persistent infection.In vitro studies indicate that Bb directly activate professional phagocytes that can efficiently phagocytose and kill both opsonized and unopsonized Bb. However, Bb exhibit an ID50 of <50 organisms in vivo, indicating that the bacteria efficiently evade phagocyte killing and suggesting that traditional in vitro models are inadequate for accurately assessing the evasion mechanisms of these fastidious spirochetes. Thus, there is an urgent need to develop techniques that allow direct assessment of the interactions between Bb and skin-associated phagocytes within living susceptible hosts.We have developed a novel system to directly visualize the behaviors of infectious Bb strains expressing fluorescence markers in situ using confocal microscopy. This model allows the acquisition of four-dimensional data reflecting Bb motility and migration in the skin of anesthetized mice during the natural course of infection. Using these techniques, our data describes the in vivo kinetics of Bb dissemination and persistence within the skin. These studies should identify Bb evasion mechanisms that can be targeted for novel curative treatments for Lyme disease. |
