Antigenic stability of Borrelia burgdorferi during chronic infections of immunocompetent mice.

Mice were actively immunized by intradermal inoculation with 10(4) cloned Borrelia burgdorferi bacteria and then cured of the B. burgdorferi infection with an antibiotic after 90 days. They were resistant to intradermal 10(2)- or 10(4)-bacterium challenge infection with either the original cloned B. burgdorferi or B. burgdorferi isolated from each punch biopsies at 90 days of infection (prior to antibiotic treatment), including autologous B. burgdorferi isolates. In contrast, sham-infected (nonimmune) mice were susceptible to challenge infection with both early and late B. burgdorferi isolates. Since there was a potential for in vitro modification of the spirochetes during the 2-week culture period which would obscure results, an alternate means of challenge infection, using tissue transplants, was implemented. By using the same approach, mice were immunized by infection, treated with antibiotics, but challenged by subcutaneous transplantation of ear skin pieces biopsied and frozen prior to antibiotic treatment. Mice were infected for 15, 90, or 180 days before biopsy and antibiotic treatment and then transplant challenged with autologous infected tissue. Sham-immunized mice received infected tissue, and immune mice received uninfected tissue as controls. Mice infected for only 15 days, but not mice infected for 90 or 180 days, could be reinfected by autografts, whereas nonimmune mice became infected with tissues collected at each of these intervals and immune mice transplanted with normal skin were uninfected. These results indicate that immunity to B. burgdorferi is effective against the original inoculum, late isolates of the spirochete, or infected tissues collected at intervals of up to 180 days, suggesting that there is no significant antigenic change in B. burgdorferi during chronic infection.