The chemokine receptor CXCR2 ligand KC (CXCL1) mediates neutrophil recruitment and is critical for development of experimental Lyme arthritis and carditis

Abstract

Deletion of the chemokine receptor CXCR2 prevents the recruitment of neutrophils into tissues and subsequent development of experimental Lyme arthritis. Following footpad inoculation of Borrelia burgdorferi, the agent of Lyme disease, expression of the CXCR2 ligand KC (CXCL1) is highly upregulated in the joints of arthritis-susceptible mice and is likely to play an important role in the recruitment of neutrophils to the site of infection. To test this hypothesis, we infected C3H KC(-/-) mice with B. burgdorferi and followed the development of arthritis and carditis. Ankle swelling was significantly attenuated during the peak of arthritis in the KC(-/-) mice. Arthritis severity scores were significantly lower in the KC(-/-) mice on days 11 and 21 postinfection, with fewer neutrophils present in the inflammatory lesions. Cardiac lesions were also significantly decreased in KC(-/-) mice at day 21 postinfection. There were, however, no differences between C3H wild-type and KC(-/-) mice in spirochete clearance from tissues. Two other CXCR2 ligands, LIX (CXCL5) and MIP-2 (CXCL2), were not increased to compensate for the loss of KC, and the production of several innate cytokines was unaltered. These results demonstrate that KC plays a critical nonredundant role in the development of experimental Lyme arthritis and carditis via CXCR2-mediated recruitment of neutrophils into the site of infection.

FIG. 1.

Ankle swelling following infection of C3H wild-type (control) and KC^−/− mice with B. burgdorferi. Mice (8/group) were 6 to 10 weeks old at the time of infection and were inoculated in the hind footpads. Data are means ± SEM and are representative of 4 separate experiments. *, significant differences from control values at the same time point (P < 0.04).

FIG. 2.

Histologic comparison of inflammatory responses in hearts and ankles of C3H and KC^−/− mice infected 21 days prior with B. burgdorferi. Representative sections were stained with H&E or subjected to immunohistochemistry to identify infiltrating neutrophils (RB6) or macrophages (F4/80). Magnification, ×100. Bar = 50 μm.

FIG. 3.

B. burgdorferi burdens in tissues of C3H wild-type and KC^−/− mice. The mice were infected via footpad inoculation, and ankles (A), hearts (B), and ears (C) were harvested on days 10, 21, and 35 postinfection. Spirochete DNA was quantified using real-time PCR for flab and normalized to murine nidogen. Data are representative of two separate experiments. Bars represent median values.

FIG. 4.

Chemokine and cytokine production in the ankles of C3H wild-type and KC^−/− mice at 11 and 21 days after infection with B. burgdorferi. Ankle joints were harvested at the indicated time points, and protein was extracted as described previously (10). Levels of KC (A), LIX (B), MIP-2 (C), IL-6 (D), IL-1β (E), and TNF-α (F) were quantified by ELISA. With the exception of KC, there were no significant differences in any of the cytokine or chemokine levels between the C3H wild-type and KC^−/− mice at either time point.

FIG. 5.

Chemokine and cytokine production in the hearts of C3H wild-type and KC^−/− mice at 11 and 21 days after infection with B. burgdorferi. Hearts were harvested at the indicated time points, and protein was extracted as described previously (10). Levels of KC (A), LIX (B), MIP-2 (C), IL-6 (D), IL-1β (E), and TNF-α (F) were quantified by ELISA. With the exception of KC there were no significant differences in any of the cytokine or chemokine levels between the C3H wild-type and KC^−/− mice at either time point.