B. burgdorferi- induced murine Lyme arthritis is dependent on TLR2 and MyD88. (A) Macroscopic score of the knees in wild-type (WT), TLR2 knockout (KO), MyD88 KO, NOD1 KO, NOD2 KO, and RICK KO mice. After 4 hours and 24 hours of intra-articular (i.a.) injection of 1 × 10^7 live B. burgdorferi, at least 10 knees per group. Data are mean ± SEM from 10 knees in each group; **P <0.01; ***P <0.0001, Mann-Whitney U test, two-tailed. (B) Scored cell influx 1 day after i.a. injection of B. burgdorferi. Data are mean ± SEM from 10 knees in each group; **P <0.01; Mann-Whitney U test, two-tailed. (C) Murine Lyme arthritis in WT, TLR2 KO, MyD88 KO, NOD1 KO, NOD2 KO, and RICK KO mice. Histology (H&E staining) 1 day after i.a. injection of B. burgdorferi in knee joints. 200× magnification; P, patella; F, femur; JC, joint cavity; SL, synovial lining. Scale bar represents 100 μM. MyD88, myeloid differentiation factor 88; NOD, nucleotide-binding oligomerization domain; RICK, serine-threonine protein kinase with a caspase activation and recruitment domain; TLR, Toll-like receptor.