Increased IL-1β gene expression in synovium and articular cartilage has previously been reported in an equine IL-1β-induced synovitis model [58] and in naturally occurring osteoarthritis [59]; however, IL-1β gene expression does not necessarily correlate with bioactive IL-1β due to the requirement for post-translational modifications such as protease cleavage to result in the secreted, bioactive form of IL-1β [60]. This evidence concerns the gene IL1B and synovitis.