Flare of antigen-induced arthritis in mice after intravenous challenge. Kinetics of antigen in the circulation and localization of antigen in the arthritic and noninflamed joint.

Intravenous injection of methylated bovine serum albumin (mBSA) in mice with unilateral, chronic, mBSA-induced arthritis has been shown to cause a flare of smouldering arthritis without affecting the contralateral, noninflamed knee joint. We studied the kinetics of 125I-labeled mBSA in the blood, and the accumulation of antigen in both arthritic and noninflamed joints. The bulk of the antigen was eliminated from the blood within 10-30 minutes, and accumulation of antigen in the joints occurred mainly within this period. The amounts of antigen found in the arthritic joints were of the same order of magnitude as the amounts found in noninflamed joints. Autoradiography of whole joint sections revealed that, in arthritic joints, antigen was located primarily at the deep capillaries and large vessels, and in the noninflamed joints, antigen was located at the small superficial capillaries. Antigen was handled by granulocytes in the arthritic joint and by synovial lining cells in the noninflamed joint. Our data indicate that tiny amounts of antigen reach the synovial stroma in both normal and arthritic joints but cause inflammation only in the arthritic joints, because of local hyperreactivity.