Abstract. We studied the influence of antigenic charge on the handling of intraarticular antigen by the joint and on the ability of the antigen to induce chronic arthritis.

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Intravenous injection of methylated bovine serum albumin (mBSA) in mice with unilateral, chronic, mBSA-induced arthritis has been shown to cause a flare of snnouldering arthritis without affecting the contralateral, noninflamed knee joint. We studied the kinetics of '251-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 1&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 primlarily at the deep capillaries and large vessels, and in thie 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 hyperreaclivity.

Mice were intravenously injected with 125I-labelled native BSA and cationic mBSA. The amount of 125I-protein in the extra- and intravascular compartment was determined in normal joints and in joints in which the vascular permeability was increased by histamine. The extravasation of BSA and mBSA is different. More BSA compared with mBSA accumulated in normal joints and the extravasation of BSA increased almost 3 times shortly after histamine injection, whereas histamine hardly affected the extravasation of mBSA.