SOCS3^ΔSB/ΔSB mice exhibit exacerbated mBSA/IL-1–induced acute arthritis. (A-D) Acute inflammatory arthritis was induced by intra-articular injection of mBSA into the knee joint followed by 3 daily subcutaneous injections of IL-1. Mice were killed on day 7. Frontal hematoxylin and eosin–stained sections through knee joints from arthritic WT (A-B) and SOCS3^ΔSB/ΔSB (C-D) mice. E indicates exudate; P, patella; PN, pannus; F, femur; and arrows, increased exudate and inflammatory cells, predominantly neutrophils, in the joint space of treated SOCS3^ΔSB/ΔSB mice. (E) Joint sections were graded for 5 features of inflammatory arthritis, each on a scale of 0 (normal) to 5 (severe) by an investigator blinded to the experimental groups. Results are shown as the mean (± SD) for 5 joints per group (*P < .05; **P < .01).