Strong inflammation is essential for expression of articular cartilage-specific citrullinated antigens

OBJECTIVETo investigate the expression of citrullinated epitopes in articular cartilage protein and whether its expression is sufficient to induce anti-citrullinated protein antibody (ACPA) response in mice. METHODSThe experimental group was treated with different concentrations of lipopolysaccharide (LPS), heat-inactivated bacteria (Escherichia coli and Staphylococcus aureus) or specific monoclonal antibody against type Ⅱ collagen to induce citrullination of articular cartilage protein, with PBS as the control. Immunohistochemistry with the monoclonal antibody ACC4 (IgG1) that specifically binds to the citrullinated epitope of cartilage protein was performed for detecting the expression of citrullinated protein, with ACC1 (IgG2a) as a positive control antibody and L243 (IgG2a) and Hy2.15 (IgG1) as the negative isotype control. In the in vivo experiment, SD rats were subjected to injection of different doses of LPS in the right knee (with PBS as the controls in the left knee), and 3 days later frozen sections