Binding of Human Urokinase Type Plasminogen Activator and Plasminogen to Borrelia Species

Borrelia burgdorferi binds human urokinase plasminogen activator (uPA), which cleaves plasminogen (Pgn) to plasmin. The ability of other Borrelia species to bind uPA, Pgn, or both was investigated. Borrelia coriacae, Borrelia garinii, Borrelia parkeri, Borrelia anserina, and Borrelia turicatae were compared with infectious and noninfectious B. burgdorferi isolates. All Borrelia species lacked endogenous proteases capable of digesting casein, but all species bound human uPA and Pgn, generating Pgn-dependent proteolytic activity. There were no significant differences in the amount of plasmin, Pgn, or uPA bound per spirochete of the different species. On unfixed borreliae, fluorochrome-conjugated uPA bound to all species. Early binding was at the terminus of B. burgdorferi, whereas diffuse binding was observed on B. coriacae, B. garinii, B. parkeri, and B. turicatae. These studies demonstrate that binding of human uPA and Pgn to borreliae occurs on multiple species with apparent differences in surface distribution.