Synovial tissue biopsy samples from healthy tissue, from psoriatic arthritis, and from rheumatoid arthritis indicated that synovium from psoriatic arthritis and rheumatoid arthritis and from mice after the induction of collagen antibody–induced arthritis stained strongly for CD248 in perivascular and fibroblast-like stromal cells. This evidence concerns the gene CD248 and rheumatoid arthritis.