Acute autoimmune collagen-induced arthritis in rabbits

Three groups of rabbits were investigated: I. 9 rabbits, immunized with rabbit collagen type I, received 1 intraarticular injection of same antigen in the right knee, and control preparations in the left knee. II. 4 rabbits, immunized with calf collagen type I, received the same intraarticular injections as in group I. III. 2 non-immunized rabbits received also the same intraarticular injections. Synovial fluid and synovium were obtained in all groups 18 hours after intraarticular injection. Knee-joints of all animals immunized and challenged intraarticularly with rabbit collagen showed strong cellular exsudation (mean 1.800 X 10(3) cells,) in contrast to control joints (mean 21 to 484 X 10(3) cells). Histologic investigation of synovium of group I animals showed in rabbit collagen injected knees in contrast to controls, vascular reactions with enlargement of small vessels, thikening of endothelial cells, perivascular infiltration and aggregation of polymorphonuclears in lumen of vessels. Intraarticular injection of rabbit collagen in calf collagen immunized rabbits, induced a limited cellular exsudation, (mean 670 X 10(3) cells) which was lower than in rabbit collagen immunized animals, however also more pronounced than in control joints. Whilst results after intraarticular injection of rabbit collagen in rabbit collagen immunized animals are interpreted as early signs of autoimmune arthritis, results after intraarticular injection of rabbit collagen in calf collagen immunized animals are regarded as milder symptoms of synovitis induced by crossreactivity of antigens.