Binding of complement regulatory protein factor H enhances serum resistance of Borrelia spielmanii sp. nov.

The European Borrelia species, B. spielmanii, has recently been shown to be associated with Lyme borreliosis/disease infections in humans. In order to elucidate complement susceptibility of diverse B. spielmanii species, we analyzed and compared two isolates obtained from patients with Lyme borreliosis for their ability to escape from complement-mediated bacteriolysis. Growth inhibition assays revealed striking differences between the two B. spielmanii isolates tested with regard to their complement sensitivity. B. spielmanii isolate A14S displayed a resistant phenotype, whereas isolate PSigII was highly sensitive to complement-mediated lysis. In addition, we demonstrate that B. spielmanii isolate A14S can bind complement regulator factor H at higher concentrations to the cell surface as compared to serum-sensitive isolate PSigII. The data presented here provide strong evidence for a correlation between factor H binding and serum resistance among the two isolates tested that can contribute to immune evasion of B. spielmanii from complement-mediated killing.