We observed that the gene expression levels of M1 macrophage markers (TNF-α, IL-1β, and iNOS) and Rspo2 were significantly enhanced, while the gene expression levels of M2 macrophage markers (IL-10 and Arg-1) were significantly inhibited in synovial tissues of osteoarthritis patients relative to those in healthy controls. Here, ARG1 is linked to osteoarthritis.