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Genetic resistance and susceptibility to experimental
Lyme arthritis have been linked with the production of interleukin-4 (IL-4) or gamma interferon (IFN-gamma), respectively. To determine the absolute requirement for these cytokines in
disease outcome, we compared arthritis development in wild-type, IL-4-deficient (IL-4 degrees ), and IFN-gamma-deficient (IFN-gamma degrees ) mice. While susceptible C3H mice developed swelling of ankle joints during the second week of infection, this swelling was exacerbated in C3H IFN-gamma degrees mice. Their arthritis severity scores at day 21, however, were similar. Resolution of arthritis was also similar between C3H and C3H IFN-gamma degrees mice. Arthritis-resistant DBA mice did not develop ankle swelling during the experimental period. There were no differences in ankle swelling or arthritis severity scores between control DBA mice and DBA IL-4 degrees mice at any of the time points tested. While the presence of spirochetes in various tissues was similar among all strains at day 21, DBA IL-4 degrees mice had a higher presence of spirochetes in blood, heart, and spleen than the DBA, C3H, and C3H IFN-gamma degrees mice did at day 60. DBA IL-4 degrees mice also had impaired ability to produce Borrelia-specific antibody responses, especially immunoglobulin G1. Thus, while IFN-gamma and IL-4 are not absolutely required for arthritis susceptibility or resistance, the production of IL-4 does appear to play an important role in Borrelia-specific antibody production and spirochete clearance.