Molecular Mechanisms Involved in Vascular Interactions of the Lyme Disease Pathogen in a Living Host

Abstract

Hematogenous dissemination is important for infection by many bacterial pathogens, but is poorly understood because of the inability to directly observe this process in living hosts at the single cell level. All disseminating pathogens must tether to the host endothelium despite significant shear forces caused by blood flow. However, the molecules that mediate tethering interactions have not been identified for any bacterial pathogen except E. coli, which tethers to host cells via a specialized pillus structure that is not found in many pathogens. Furthermore, the mechanisms underlying tethering have never been examined in living hosts. We recently engineered a fluorescent strain of Borrelia burgdorferi, the Lyme disease pathogen, and visualized its dissemination from the microvasculature of living mice using intravital microscopy. We found that dissemination was a multistage process that included tethering, dragging, stationary adhesion and extravasation. In the study described here, we used quantitative real-time intravital microscopy to investigate the mechanistic features of the vascular interaction stage of B. burgdorferi dissemination. We found that tethering and dragging interactions were mechanistically distinct from stationary adhesion, and constituted the rate-limiting initiation step of microvascular interactions. Surprisingly, initiation was mediated by host Fn and GAGs, and the Fn- and GAG-interacting B. burgdorferi protein BBK32. Initiation was also strongly inhibited by the low molecular weight clinical heparin dalteparin. These findings indicate that the initiation of spirochete microvascular interactions is dependent on host ligands known to interact in vitro with numerous other bacterial pathogens. This conclusion raises the intriguing possibility that fibronectin and GAG interactions might be a general feature of hematogenous dissemination by other pathogens.

Enhanced Adhesion and OspC Protein Synthesis of the Lyme Disease Spirochete Borrelia Burgdorferi Cultivated in a Host-Derived Tissue Co-Culture System

“…These observations indicated that early-stage interaction events were essential for sustained association and vascular escape. These observations also demonstrated that microvascular interactions were dependent on B. burgdorferi proteins expressed only in the infectious strain (32). These findings are in agreement with our adhesion assay; infectious spirochetes bind more avidly to HUVEC monolayers.…”

“…Protein A-immunogold labelling by using antiOspC monoclonal antibodies (G7) the spirochetes. It has been demonstrated that B. burgdorferi isolated from ticks fed on humans can express both OspA and OspC proteins and that regulation of the expression of these proteins is phenotypically different (31)(32). Human isolates of B. burgdorferi contain this protein in contrast to tick isolates which only synthesize OspA and OspB proteins.…”

“…Regarding to the role of OspC protein in the infection process of B. burgdorferi in humans and animals, there were other studies; Researchers have studied the molecular mechanisms involved in vascular interactions of the Lyme disease bacterium in vivo (32). They engineered a fluorescent strain of B. burgdorferi, and visualised its dissemination from the microvasculature of living mice using intravital microscopy.…”

Live imaging reveals a biphasic mode of dissemination of Borrelia burgdorferi within ticks

“…The linkage between motility and infectivity for mammals recently was strengthened by intravital imaging of blood-borne spirochetes in mice; following attachment to the vascular endothelium, B. burgdorferi move toward and then rapidly penetrate endothelial cell junctions (63,64). Previous attempts to elucidate the mechanisms of spirochete dissemination within the arthropod have employed fixation and microscopic techniques that preclude analysis of the dynamic interactions between pathogen and vector (19,20,37).…”

Borrelia burgdorferi Needs Chemotaxis To Establish Infection in Mammals and To Accomplish Its Enzootic Cycle

“…First, B. burgdorferi has the ability to swim in highly viscous gel-like media (20,24), including the connective tissue, and this ability is abrogated in aflagellated nonmotile mutants of B. burgdorferi (29,35,48). Second, real-time intravital microscopy analysis revealed that B. burgdorferi is able to penetrate the endothelium of blood vessels and quickly disseminate from the microvasculature in living mice and that the translational motility appears to be essential for transendothelial migration (34,39). Third, a recent report indicates that B. burgdorferi transitions from a nonmotile phase to a motile phase during the period when the spirochete penetrates the tick gut basement membrane and migrates to the salivary glands of feeding ticks (14).…”