Induction of IgM autoantibody production after B. burgdorferi infection in Myd88 KO mice. RF, anti-dsDNA, and anti-thyroglobulin IgM antibody levels were measured by ELISA. Values represent the mean optical densities ± SD observed for the 1/100 (RF), 1/500 (anti-dsDNA), or 1/100 (anti-thyroglobulin) serum dilution, respectively. The same dilution for MRL/lpr pooled serum as that used for MyD88+/− and MyD88KO mice was used as a positive control. Five animals were tested in each group except for infected MyD88 KO mice (six animals).