IL-22 expression is increased variedly in the initial phase, onset and chronic phase of a pristane-induced arthritis rat model

The aim of the present study was to investigate the expression pattern of T helper (Th) 17 and Th22 cell-related factors in a pristane-induced arthritis (PIA) rat model. PIA rats were divided into the initial phase group [day (D) 6 post-pristane injection], the onset of clinical arthritis group (D12), the acute arthritis group (D26) and the chronic arthritis group (D70). Rats injected with saline alone were used as the control group. The mRNA expression levels of interleukin (IL)-17A, IL-17F, interferon (IFN)-γ, IL-22, IL-22 receptor (R) 1, IL-22 binding protein (BP) and RAR-related orphan receptor α were examined in the spleen and/or synovium of the various phases of PIA rats by reverse transcription-quantitative polymerase chain reaction analysis. The results demonstrated that, in the spleen, IL-22 exhibited an increasing trend in both the initial phase and the onset of disease, while the ratio of IL-22R1/IL-22BP increased in both phases, compared with the control group. During the acute arthritis phase, IL-17F and IFN-γ were significantly increased and IL-17A exhibited an increasing tendency in the synovium, compared with the control group. In the chronic phase, IL-22, IL-22R1 and IFN-γ were increased in the spleen, while IL-22 exhibited an increasing trend in the synovium. In addition, immunohistochemistry analysis was used to evaluate the expression of IL-17A, IL-21, IL-22 and IL-22R1 in the ankle joints of D26 PIA rats. IL-17A was mainly expressed in infiltrated inflammatory cells in the synovium. IL-21 and IL-22 were both expressed in the infammatory cells and in the articular chondrocyte of the proliferative zone. IL-22R1 was expressed in proliferating synovial cells. In conclusion, Th17 and Th22-related factor expression varied in different disease progression phases and in different tissues in PIA rats. IL-22 expression exhibited an increasing trend in the initial phase and the onset phase of arthritis and increased significantly with progression to chronic arthritis in the PIA rat model. It is thought that IL-22 may serve an important role in the pathological process of PIA, particularly in the chronic fluctuation phase. Therefore, it may be a candidate molecule for the treatment of rheumatoid arthritis.