Antigen induced arthritis is a unilateral T-cell driven model caused by direct injection of an antigen into the knee joint of a FCA preimmunized animal. The chronicity is determined by antigen retention in avascular structures of the joint through charge mediated binding or antibody mediated trapping. Cationicity of the antigen is a prerequisite in this model in the mouse and commercial mBSA is a suitable antigen. Cartilage erosive character is strongly enhanced in the presence of marked antibody titer. Concomitant boosting of the immune response with Bordetella pertussis adds to this. T-cell mediated flares can be induced by local or systemic rechallenge with low dose antigen, and display a strong erosive phenotype.