Imbalance of M1/M2 macrophages is linked to severity level of knee osteoarthritis

Macrophages, whether M1 or M2 subtype, have been found to be implicated in the pathogenesis of osteoarthritis (OA). However, no study regarding the status of M1 and M2 macrophages has been reported in knee OA. To investigate the status of M1 and M2 macrophages in knee OA, synovial fluid as well as peripheral blood were collected from 80 patients with knee OA and 80 healthy controls. Reverse transcription-quantitative PCR was used to quantitatively detect the expression of CD11c as a marker for M1 macrophages and CD206 as a marker for M2 macrophages from synovial fluids. As confirmation, flow cytometry was employed to count the number of monocytes from whole blood using the CD86 (M1) and CD163 (M2) markers on monocytes. The ratio of M1 to M2 macrophages was shown to be markedly higher in knee OA than that of control and that the ratio was significantly positively correlated with level of Kellgren-Lawrence grade in knee OA, that is, the higher the ratio the more severe the knee OA seems to be. Thus, our study presented direct evidence for the involvement of macrophages in the pathogenesis of knee OA.