Salp15 inhibits the killing of serum sensitive Borrelia burgdorferi sensu lato isolates

Department of Medical Microbiology, Leiden University Medical Centre, Leiden, The Netherlands; Center for Experimental and Molecular Medicine, (CEMM) University of Amsterdam, AMC, Amsterdam, The Netherlands; Section of Infectious Diseases, Department of Internal Medicine, Yale University School of Medicine, New Haven, Connecticut

^* To whom correspondence should be addressed. Email: T.J.Schuijt{at}lumc.nl.

	Abstract

Borrelia burgdorferi, the agent of Lyme disease is transmitted by ticks. During transmission from the tick to the host, spirochetes are delivered with tick saliva, which contains the salivary protein Salp15. Salp15 has been shown to protect spirochetes against B. burgdorferi-specific antibodies. We now show that Salp15 from both Ixodes ricinus and Ixodes scapularis protect serum sensitive isolates of Borrelia burgdorferi sensu lato against complement-mediated killing. I. ricinus Salp15 showed stronger protective effects compared to I. scapularis Salp15. Deposition of terminal C5b-9 complement complexes, part of the Membrane Attack Complex, on the surface of B. burgdorferi was inhibited in the presence of Salp15. In the presence of normal human serum, serum sensitive Borrelia burgdorferi require protection against complement-mediated killing, which is provided, at least in part, by the binding to the tick salivary protein Salp15.