Roles of OspA, OspB, and flagellin in protective immunity to Lyme borreliosis in laboratory mice

Vaccination with recombinant outer surface protein A (OspA) has been shown to protect mice from infection with Borrelia burgdorferi, the Lyme disease agent. To determine whether antibodies to B. burgdorferi proteins other than OspA are involved in protective immunity, antibodies to OspA were removed from protective anti-B. burgdorferi serum; the residual serum was still protective. Absorption of OspA and OspB antibodies from anti-B. burgdorferi serum eliminated the protective effect. Therefore, active immunization experiments were performed to determine the roles of OspB and flagellin in protective immunity and to determine whether protective immunity induced by OspA is dose dependent. Active immunization with recombinant OspA protected mice from infection with an inoculum of 10⁴ spirochetes, but this protection could be overcome with a challenge of 10⁷ spirochetes; OspB protected mice from infection with an inoculum of 10³ spirochetes but was insufficient to fully protect against 10⁴ organisms; and immunization with flagellin had no protective effect. These studies suggest that OspA and OspB, but not flagellin, play roles in protective immunity to spirochete infection.