FIG. 6.

B. burgdorferi-infected mice develop arthritis and carditis in the absence of IL-18. IL-18^−/− mice and their wild-type littermates (IL-18^+/+) were infected with B. burgdorferi as described in Materials and Methods and sacrificed 3 weeks after infection, and their joints and hearts were processed for either histology or DNA isolation. Representative HE-stained sections of joints (A to D) and heart (E and F) of both wild-type (A, B, and E) and IL-18^−/− (knockout) (C, D, and F) mice are shown. B and D are the magnified pictures of the boxed areas of A and B, respectively. The insets are the magnified views of the areas in the boxes. (G) DNA was isolated from joints of IL-18^−/− (n = 6) and wild-type (n = 5) mice and processed to quantitate B. burgdorferi DNA levels using real-time RT-PCR for a single-copy B. burgdorferi gene, recA. Numbers represent copies of B. burgdorferi recA normalized to the weight of tissue used to isolate DNA.