INVASION OF HUMAN NEURONAL AND GLIAL CELLS BY AN INFECTIOUS STRAIN OF BORRELIA BURGDORFERI Jill A. Livengood, Robert D. Gilmore Jr.* CENTERS for DISEASE CONTROL AND PREVENTION, Division of Vector-borne Infectious Diseases, 3150 Rampart Road, CSU Foothills Campus, Fort Collins, CO 80522, USA Received 13 June 2006; accepted 30 August 2006 Abstract Human infection by Borrelia burgdorferi, the etiological agent for Lyme disease, can result in serious acute and late-term disorders including neuroborreliosis, a degenerative condition of the peripheral and central nervous systems. To examine the mechanisms involved in the cellular pathogenesis of neuroborreliosis, we investigated the ability of B. burgdorferi to attach to and/or invade a panel of human neuroglial and cortical neuronal cells. In all neural cells tested, we observed B. burgdorfer in association with the cell by confocal microscopy. Further analysis by differential immunofluorescent staining of external and internal organisms, and a gentamicin protection assay demonstrated an intracellular localization of B. burgdorferi. A non-infectious strain of B. burgdorferi was attenuated in its ability to associate with these neural cells, suggesting that a specific borrelial factor related to cellular infectivity was responsible for the association. Cytopathic effects were not observed following infection of these cell lines with B. burgdorferi, and internalized spirochetes were found to be viable. Invasion of neural cells by B. burgdorferi provides a putative mechanism for the organism to avoid the host's immune response while potentially causing functional damage to neural cells during infection of the CNS. Keywords: Borrelia burgdorferi; Cell invasion; Neuroborreliosis Corresponding author. Tel.: +1 970 221 6405; fax: +1 970 221 6476. Copyright © 2006 Elsevier B.V.