AbstractObjectiveTo examine the capacity of T cell interleukin‐17A (IL‐17A; referred to hereinafter as IL‐17) to induce cartilage damage during experimental arthritis in the absence of IL‐1.MethodsLocal IL‐17 gene transfer was performed in the knee joint of IL‐1–deficient mice and wild‐type controls during streptococcal cell wall (SCW)–induced arthritis. Knee joints were isolated at various time points for histologic analysis of cartilage proteoglycan (PG) depletion. Expression of messenger RNA for inducible nitric oxide synthase, matrix metalloproteinases (MMPs) 3, 9, and 13, and ADAMTS‐4 was determined by quantitative polymerase chain reaction analysis. VDIPEN staining was analyzed to study MMP‐mediated cartilage damage. In addition, systemic anti–IL‐1α/β antibody treatment was performed in mice immunized with type II collagen and injected locally with an adenoviral vector expressing IL‐17 or with control adenovirus. Knee joints were isolated and analyzed for cartilage PG depletion, chondrocyte death, and cartilage surface erosion.ResultsDuring SCW‐induced arthritis, local T cell IL‐17 gene transfer turned this acute, macrophage‐driven joint inflammation into a severe, chronic arthritis accompanied by aggravated cartilage damage. Of high interest, the IL‐1 dependency of cartilage PG depletion was fully abrogated when IL‐17 was locally overexpressed in the joint. Moreover, local IL‐17 gene transfer increased MMP expression without the need for IL‐1, although IL‐1 remained essential for part of the cartilage VDIPEN expression. Furthermore, when IL‐17 was overexpressed in the knee joints of mice with collagen‐induced arthritis, anti–IL‐1 treatment did not reduce the degree of chondrocyte death or cartilage surface erosion.ConclusionThese data show the capacity of IL‐17 to replace the catabolic function of IL‐1 in cartilage damage during experimental arthritis.