ABSTRACT
Objective To demonstrate high mobility group box chromosomal protein 1(HMGBI) expression in synovium and joint,and to identify the role of HMGB1 in the pathogenesis of synovitis and joint destruction in adjuvant-induced arthritis(AA).Methods AA of 15 male rats were induced in SD rats by intradermal injection of 100?l Freud's complete adjuvant in the foot pad of the left hind paw.All rats were killed at the 18th day.Synovium and joints were collected for histopathology studies and determining the expression of HMGB1 by immunohistochemistry,and serum was collected for determining the expression of HMGB1 by western blotting analysis.Results Immunostaining of specimens from normal rats showed that HMGB1 was primarily confined to the nucleus of synoviocytes with occasional cytoplasmic staining.In contrast, inflammatory synovial tissues from AA rats showed a distinctly different HMGB1 staining pattern.Nuclear HMGBI expression was accompanied by a cytoplasmic staining in many mononuclear cells.The cytoplasmic HMGB1 expression in synovium of AA rats is significantly higher than that of normal rats.Additionally,HMGBI was highly expressed in the nuclei and cytoplasm of the subchondral chondrocytes and inflammatory cells in bone erosion in AA rats(P＜0.01),while fewer positive cytoplasmic staining of HMGB1 was found in chondrocytes and fewer positive nuclear staining was found in bone cells in normal rats.HMGB1 concentration was significantly higher in serum of AA rats than that in normal rats(P＜0.001).Conclusion The cytoplasmic HMGBI expression in synovium and joints is greatly upregulated;the level of HMGB1 in serum is increased in AA rats which suggests a patbogenetic role of HMGB1 in synovitis and bone destruction of adjuvant-induced arthritis.