Antigen-induced arthritis: inflammation and antigen handling after two different doses of intra-articularly injected antigen.

We studied (i) the inflammatory response induced by intra-articular (i.a.) injection of 2.5 and 0.5 mg 125I-labelled bovine serum albumin (125I-BSA) into the paired knee joints of rabbits immunized with BSA in Freund's complete adjuvant, and (ii) handling of these different doses of antigen by means of regular external radioactivity measurements. The joint inflammation was quantified by 99mTechnetium pertechnetate uptake measurements. More severe arthritis was seen in the 2.5 mg BSA-injected than in the paired 0.5 mg BSA-injected knee, both in the early and in the late phase of antigen-induced arthritis. External radioactivity measurements showed enhanced disappearance of radioactivity from the 2.5 mg 125I-BSA challenged knee joint, resulting in lower percentual retention of the dose injected than in the 0.5 mg injected knee joint. However the calculated absolute amount of long term retained BSA in the 2.5 mg BSA injected knee, 4 weeks after i.a. injection, was still about 2.8 times the quantity of BSA retained in the 0.5 mg BSA-injected paired knee joint. These data indicate that the severity of both the early and late phase of antigen-induced arthritis is i.a. antigen dose-dependent and, in addition, suggest that handling of i.a. antigen depends in part on the severity of joint inflammation.