Experimental arthritis produced by injection of mediators of delayed hypersensitivity.

Synovitis was produced in the rabbit knee by repeated intraarticular injection of a preparation of mediators of cellular immunity. The mediators were prepared by incubation of KLH with lymph node cells of animals previously immunized with KLH in Freund's adjuvant. Following three intraarticular injections, a chronic synovitis resulted in which hyperplasia of the lining layer and infiltration of the sublining layer occurred. The cell types in the sublining layer were predominantly histiocytes and fibroblasts. These experiments demonstrate that mediators of cellular immunity may produce a chronic inflammatory reaction when injected repeatedly into normal joints. They indicate that the cellular immune response may play a role in the development of the synovitis of immunologically induced arthritides.