Establishment Of Rat Collagen-induced Arthritis Model And Evaluation Of Interleukin-33 Expression In Synovial Tissue

Objective: To optimize procedures for reproducible collagen-induced arthritis(CIA) models in rats with high incidence, in terms of the collagen doses and gender factor. And to investigate the expression of interleukin-33(IL-33) in CIA synovial tissue comparing to normal synovium.Method: The inbred Wistar rats were immunized by intradermal injection of chicken collagen type II(CII) emulsified with incomplete Freund's adjuvant(IFA) to induce CIA. The rats in study were randomly divided into 8 groups. Four different doses (400μg, 300μg, 200μg, 0μg) and gender factors were taken into account. Every week,volume of paws was measured and arthritis severity scores were recorded.Every 2 weeks, CII-specific antibody and TNF-αin serum were evaluated by ELISA.At the 6th week since first injection X-ray photographs were taken then animals were sacrificed.The pathological characteristics and bone erosion of the joints were checked by histopathological techniques.IL-33 expression in CIA synovial tissue as well as in normal synovium was investigated with semiquantitative RT-PCR and immunohistochemistry.Results: Lose of weights,erythema and swelling of paws involving the ankle, foot, and digits in CIA rats were observed.The inflamed paws limited the animal's mobility and couldn't support the body weight at the peak of disease severity. Average severity score could reach 6.3±1.8. The serum CII-specific antibody and TNF-αlevel both elevated in CIA rats compared with the normal ones.At the 6th week since first injection, X-ray photograph and histopathological techniques showed typical chronic synovial inflammation with bone erosion.Statistic analysis indicated that CIA incidence rised with the dose of CII injection and the 400μg group's incidence could reach 100%,while gender factor showed no remarkable effect.None of the rats were died of collegen injection during this study.CIA synovial tissue displayed a stronger IL-33 expression than normal synovial at both mRNA and protein levels. Immunohistochemistry staining for IL-33 protein were mainly found in endothelial cells, fibroblasts and synovial lining cells. Normal synovial tissue showed a lighter staining than CIA ones.Conclusion:1. We had successfully established reproducible CIA models in rats with high incidence, typical clinical symptoms and pathological characteristics indicating chronic synovial inflammation with bone erosion were observed.2. Rising the dose of collagen injection could improve CIA incidence while gender factor had no remarkable influence on it. 400μg CII per rat could reach 100% incidence.3. IL-33 is constitutively expressed at low levels in endothelial cells, fibroblasts and synovial lining cells in normal synovial tissue.4. CIA synovium displayed a stronger IL-33 expression than normal ones, suggesting that IL-33 might play an important role in chronic inflammation diseases.