Exacerbation of antigen-induced arthritis after challenge with intravenous antigen

The occurrence and morphology of flare-up of arthritis after intravenous (i.v.) antigen administration was investigated in mice with on-going antigen-induced arthritis (AIA). Intravenous injection of 300 micrograms methylated bovine serum albumin (mBSA) in mice with unilateral arthritis induced by mBSA, elicited 6 weeks previously, caused clear flare-up of the smouldering joint inflammation without affecting the contralateral non-arthritic knee joint. Histological signs of the flare-up reaction were already present at 6 hr after i.v. challenge and lasted for at least 4 days. Characteristic features are the presence of large numbers of granulocytes just beneath the synovial lining layer, inflammatory foci in adjacent periarticular tissues, and deposits of fibrin-like material in the joint space. Variations in the severity of the preceding arthritis and in the interval (4-12 weeks) between AIA induction and i.v. challenge had no major influence on the occurrence and degree of the flare-up phenomenon. Since exacerbations of joint inflammation are seen in rheumatoid arthritis, this phenomenon may be of importance in this disease.