T-Cell-independent responses to Borrelia burgdorferi are critical for protective immunity and resolution of lyme disease

The humoral immune response to Borrelia burgdorferi during persistent infec tion is critical to both protective and disease-resolving immunity. This st udy examined the role of B cells in the absence of T cells during these eve nts, using mice with selected immune dysfunctions. At 6 weeks postinfection ,lan interval at which arthritis resolves in immunocompetent mice, arthriti s severity was equivalent among immunocompetent mice, alpha beta(+)-T-cell- deficient mice, and mice lacking both alpha beta(+) and gamma delta(+) T ce lls. Arthritis severity was worse in SCID mice, which lack T and B lymphocy tes. Carditis regressed in immunocompetent mice and those lacking both alph a beta(+) and gamma delta(+) T cells but remained active in mice lacking on ly alpha beta(+) T cells and in SCID mice, Mice lacking only alpha beta(+) T cells and those lacking both alpha beta(+) and gamma delta(+) T cells gen erated immunoglobulin M (IgM) and IgG3 B. burgdorferi-reactive antibodies. Sera from infected immunocompetent mice, mice lacking only alpha beta(+) T cells, and mice lacking both alpha beta(+) and gamma delta(+) T cells passi vely protected naive mice against challenge inoculation with B. burgdorferi . However, only sera from infected immunocompetent mice, but not sera from infected T-cell-deficient mice, were able to resolve arthritis when passive ly transferred to actively infected SCID mice. These data demonstrate that B-cell activation during a T-cell-independent response may be critical for resolution of arthritis and carditis and that protective antibodies are gen erated during this response.