Interleukin-17B is an approximately 20 kDa glycosylated cytokine that plays a role in inflammation and bone growth. IL-17B binds to IL-17 RB and induces the production of inflammatory cytokines and the infiltration of inflammatory immune cells. It is expressed in the central nervous system, testis, ovary, stomach, pancreas, and small intestine. In the skeletal system, IL-17B is expressed in bone collars surrounding primary ossification centers as well as in epiphyseal plate chondrocytes during development and after bone fracture. IL-17B is upregulated in arthritic cartilage where it exacerbates the severity of disease. It is also upregulated in aggressive breast cancer cell lines, and its exaggerated signaling through IL-17 RB promotes tumorigenicity.