Influence of x-ray treatment on antigen-induced experimental arthritis

Six groups of 3 rabbits each were immunised with ovalbumin and received one intra-articular injection of antigen. The animals of 3 groups received local x-ray irradiation of 600 rads for 8 minutes to the right knee joint 12 days after the intra-articular challenge. Animals of the other 3 groups were not irradiated. The antigen-induced arthritis was investigated by determining the exudation is synovial fluid and by histological study of the synovium examined 48 hours, 7 days, and 4 weeks after the irradiation date. All animals in the nonirradiated groups showed a distinct chronic synovitis. Irradiated animals showed almost no synovitis 48 hours and 7 days following irradiation. In 2 rabbits synovitis had reappeared 4 weeks after irradiation with findings similar to those in the control groups. Only one animal still showed an inhibition of synovitis. X-ray irradiation of non-challenged knees did not induce any pathological changes. This time-limited effect of one local irradiation on antigen-induced arthritis seems to be mainly an anti-inflammatory action. Local immunological inhibition might possibly operate too. X-ray induced inhibition of synovitis is compared with the effect of locally injected radiocolloids.