OspA vaccination of mice with established Borrelia burgdorferi infection alters disease but not infection.

C3H mice were actively immunized with outer surface protein A (OspA) at different intervals after infection with Borrelia burgdorferi to determine the effect of postexposure vaccination on the course of murine Lyme borreliosis. Mice were vaccinated with an OspA-glutathione transferase fusion protein or glutathione transferase (control) in complete Freund's adjuvant; vaccination was followed by two weekly booster injections in incomplete adjuvant. Two weeks after the final booster injection, organs were cultured for B. burgdorferi (blood, spleen, skin, and bladder) and examined for histopathology (joints and hearts). When vaccination was commenced in the early stages (5 to 14 days) of infection, active immunization with OspA partially cleared spirochetes from the bloodstream but did not eliminate them from other tissues or alter the course of joint or heart disease. Commencement of vaccination at 60 days after infection (at which time joint or heart disease is resolving), however, reduced both the number of mice and individual joints with arthritis, a result suggesting an acceleration of the resolution phase of the disease. Postexposure immunization with OspA may partially alter the course of murine Lyme arthritis but does not eliminate infection.