The generation of enzymatically active plasmin on the surface of spirochetes

The spirochete Borrelia burgdorferi, the etiologic agent of Lyme disease, i s transmitted to the host by a feeding Ixodid tick. The spirochete subseque ntly disseminates through the shin, enters the Bloodstream, and becomes sys temic. A potential mechanism for this invasiveness was identified with the discovery that B. burgdorferi can bind components of the plasminogen activa tion system (PAS). The methodology for analyzing the generation of enzymati cally active plasmin on the surface of this organism is given, and applied to measure spirochete viability, strain differences, and breakdown of extra cellular matrix (ECM) macromolecules, Plasmin acquisition by B. burgdorferi was measured photometrically by a specific chromogenic substrate. The grow th of B. burgdorferi in culture was not affected by the presence of active plasmin on the spirochete surface. Plasmin-coated B. burgdorferi degraded t he purified (ECM) components fibronectin, laminin, and vitronectin, but not collagen. The addition of B. burgdorferi with surface plasmin to a radiola beled, native ECM resulted in degradation of noncollagenous protein, as mea sured by release of solubilized radioactivity. Breakdown of purified ECM co mponents or native ECM did not occur after exposure to untreated spirochete s or spirochetes treated with uPA or PLG alone: These results provide in vi tro evidence that enzymatically active plasmin on the surface of B, burgdor feri may be partially responsible for its invasiveness. (C) 2000 Academic P ress.