Experimental arthritis, light and electron microscope studies of antigen and antibody using horseradish peroxidase as antigen.

Experimental arthritis was produced by the intra-articular injection of horseradish peroxidase into rabbits previously immunized with this antigen. The distribution of antigen and specific antibody was studied by light and electron microscopy. This has not allowed, as had been hoped, the unequivocal detection of antigen beyond the first week after induction of arthritis. Antibody was demonstrated in the synovium 1, 2, 4 and 12 weeks after induction of arthritis. This was located mostly in plasma cells and the extracellular spaces, in close association with collagen fibres. Further experiments suggest that this extracellular antibody is neither firmly bound to the collagen nor present as immune complexes.