ARG1 and osteoarthritis: Consistent with previous reports [7], the expression of M1 type macrophage markers (TNF-α, IL-1β, and iNOS) in osteoarthritis patients’ synovial tissue were significantly higher, while the expression of M2 type macrophage markers (IL-10 and Arg-1) in osteoarthritis patients’ synovial tissue were significantly lower than that in normal synovial tissue, which suggested M1 macrophages were mainly accumulated in the synovium of osteoarthritis patients.