Provided are a therapeutic agent and a preventive agent for osteoarthritis and osteoarthritic inflammation (synovitis). The invention is based on a finding that symptoms of osteoarthritis can be relieved using an IgM‑type anti-Fas antibody. More specifically, the invention is based on a finding that production of a cartilage matrix degrading enzyme can be inhibited using an IgM‑type anti-Fas antibody. Also, the invention is based on a finding that cartilage matrix productivity can be improved using an IgM‑type anti-Fas antibody.
