Журнал биотерроризма и биозащиты

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Virulence Factors Involved in Passage of Francisella tularensis subsp. novicida Through an Air-Blood Barrier Model

Sandra S Ojeda, Chris A Mares, Jorge I Alvarez, Qun Li, Carlos J Orihuela and Judy M Teale,

Francisella tularensis subsp. novicida ( F. novicida ) is a facultative intracellular pathogen that when inhaled causes respiratory infection in mice; it is widely used as a model to study tularemia caused by F. tularensis. F. novicida is able to infect different cell types including macrophages and dendritic cells. In the present study we examined F. novicida interactions with human lung epithelial cells and determined the role of established virulence determinants in these processes. A549 type II lung epithelial cells and murine LA-4 bronchial epithelial cells were used to examine the ability of wild type F. novicida and the mutant F. novicida strains deficient in IglC, Tul4, MglA, 58kDa membrane lipoprotein, and RipA to adhere, invade, replicate within, and translocate through an in vitro transwell system. Using this systematic approach, we determined that different virulence factors play cell-site specific roles during infection: Tul4 is important for adhesion to lung cells; MglA, 58kDa protein, and Tul4 are important for cell invasion; IglC and its transcriptional regulator MglA are important for intracellular replication; and the function of MglA is required for migration across cell barriers. In addition we also determined that F. novicida infection results in upregulation of matrix metalloprotease 9 (MMP-9) by lung epithelial cells and the subsequent disruption of cell adherens junctions as characterized by loss of cadherin, alpha and beta catenin, and the basal membrane protein laminin.

We conclude that F. novicida is able to attach, invade, and cross through lung epithelial cells and that these properties are determined by individual virulence determinants.