Rabbit arthritis induced by cell-free extracts of erysipelothrix

A cell-free crude extract of Erysipelothrix rhusiopathiae injected intravenously in rabbits induced pathological lesions of the synovial tissue similar to the lesions seen in rheumatoid arthritis. Fluorescence techniques utilizing tagged specific antiserum and fluorescent-tagged antigen injected into nonsensitized rabbits demonstrated the localization of antigen exclusively in the synovium. Localized concentration of fluorescence was demonstrated as early as 1 hr after injection, before histological changes were apparent. After 48 hr, the fluorescence was concentrated in focal areas and early pathological changes characterized as "mesenchymal activation" were observed. A consideration of the significant role of exogenous antigen in the sensitivity arthritides is discussed.