Spontaneous Arthritis Development in CD11c-Flip-KO Mice

CD11c-Flip-KO and the littermates were assessed for the spontaneous development of arthritis on a weekly basis from 4 to 36 weeks of age. The clinical severity score was defined as the sum (maximum=28) of joint swelling/inflammation (0–3 each of four paws/ankles), joint deformity (including toe flexion, contraction and shortening, 0–3 of each of four paws/ankles) and the grip strength (on a 3-mm diameter of wires, 0–4 per mouse)57 (link). The clinical incidence was defined as any mouse with clinically observed joint swelling/inflammation ≥1. The histologic analysis was performed utilizing paraffin-embedded sections of interphalangeal joints of the back and front paws, ankles and knees subjected to haematoxylin and eosin (H&E) staining58 (link). H&E ankle sections were evaluated by a blinded pathologist for inflammation (0–5), bone erosion (0–5), pannus formation (0–5) and median synovial lining thickness, neutrophil infiltration and cartilage destruction58 (link)59 (link). Macrophages in ankles were identified with immunohistochemistry staining by the Northwestern University Mouse Histology & Phenotyping Laboratory employing anti-F4/80 (eBioscience, cat. no. 14–4801, 1:1,000) or isotype-matched control IgG (eBioscience, cat. no. 16–4321) antibodies.