Histopathology of joints from SOCS-1+/+ IFN-γ–/– and SOCS-1–/– IFN-γ–/– mice. Acute inflammatory arthritis was induced by intra-articular injection of 200 μg mBSA into the knee joint followed by three daily subcutaneous injections of 20 ng IL-1β. Mice were sacrificed on day 7, knee joints were fixed in 10% formalin, and H&E-stained frontal sections were prepared. Knee joints were taken from nonarthritic SOCS-1–/– IFN-γ–/– mice (a and b), arthritic SOCS-1+/+ IFN-γ–/– mice (c and d), and arthritic SOCS-1–/– IFN-γ–/– mice (e and f). Magnification: a, c, and e, ×40; b, d, and f, ×100.