Intravital imaging of Borrelia burgdorferi and murine innate immune cells during early cutaneous infection. (37.42)

Abstract

After tick transmission, the spirochete, Borrelia burgdorferi (Bb), remains at the skin inoculation site for up to 48 hours before spreading and causing Lyme disease. Bb surface agonists should elicit potent inflammation and clearance in skin. However, the ID50 is <50 Bb, indicating efficient immunoevasion and suggesting that traditional in vitro models are inadequate for accurately characterizing Bb pathogenesis (i.e. most models display efficient Bb clearance by phagocytes). Thus, we have devised a confocal microscopy method for visualizing infectious fluorescent Bb in situ and in real-time. Here, we inject Bb into ear skin of anesthetized mice and collect four-dimensional data regarding Bb motility during natural infection. This data is complemented by quantitative PCR and histological analyses of the temporal fall and rise of spirochete numbers in vivo. By 4h, the majority of Bb at the injection site are immobile, while Bb adjacent to the site are highly motile. Two movement types are seen: 1) a back and forth shift that may aid Bb in finding an optimal migration path and 2) a directed run that navigates dermal structures. Analysis indicates an average Bb velocity of ≥100 um per minute in skin, which is >10x faster than any immune cell velocities observed in our model. This suggests that Bb motility is a primary mechanism for host cell evasion and indicates our imaging techniques will allow true delineation of host-Bb interactions critical for Lyme disease development.