Fig. 1

Borrelia burgdorferi causes severe arthritis. a Development of hind tibiotarsal joint swelling was monitored once a week by measuring the mediolateral diameter of the joint. The results from B. burgdorferi-infected mice are compared with those from uninfected mice. Values are mean ± SD; number of analyzed joints: infected (n = 8–28), uninfected (n = 8). *P < 0.05. b Representative images of tibiotarsal joints from a B. burgdorferi-infected (upper left) and an uninfected control (upper right). Lower insets show the indicated areas of infected mouse at higher magnification. Severe arthritis is seen in the infected mouse, with synovial proliferation (arrow in lower left image) and infiltration of inflammatory cells (asterisk in lower right image). Hematoxylin and eosin staining of paraffin-embedded 5-μm synovial tissue sections at × 50 and × 100 original magnification