Dynamics of Borrelia Burgdorferi Invasion and Intravasation in a Tissue Engineered Dermal Microvessel Model

Abstract Lyme disease is a tick-borne disease prevalent in North America, Europe, and Asia. Dissemination of vector-borne pathogens, such as Borrelia burgdorferi ( Bb ), results in infection of distant tissues and is the main contributor to poor outcomes. Despite the accumulated knowledge from epidemiological, in vitro , and in animal studies, the understanding of dissemination remains incomplete with several important knowledge gaps, especially related to invasion and intravasation at the site of a tick bite, which cannot be readily studied in animal models or humans. To elucidate the mechanistic details of these processes we developed a tissue-engineered human dermal microvessel model. Fluorescently-labeled Bb (B31 strain) were injected into the extracellular matrix (ECM) of the model to mimic tick inoculation. High resolution, confocal imaging was performed to visualize Bb migration in the ECM and intravasation into circulation. From analysis of migration paths we found no evidence to support adhesin-mediated interactions between Bb and components of the ECM or basement membrane, suggesting that collagen fibers serve as inert obstacles to migration. Transendothelial migration occurred at cell-cell junctions and was relatively fast, consistent with Bb swimming in ECM. In addition, we found that Bb alone can induce endothelium activation, resulting in increased immune cell adhesion but no changes in global or local permeability. Together these results provide new insight into the minimum requirements for dissemination of Bb at the site of a tick bite, and highlight how tissue-engineered models are complementary to animal models in visualizing dynamic processes associated with vector-borne pathogens. Significance Statement Using a tissue-engineered human dermal microvessel model we reveal new insight into the invasion and intravasation of Borrelia burgdorferi ( Bb ), a causative agent of Lyme disease in North America, following a tick bite. These results show how tissue-engineered models enable imaging of dynamic processes that are challenging in animal models or human subjects.