Studies on adjuvant‐induced polyarthritis in rats. I. Adjuvant composition, route of injection, and removal of depot site

The composition and quantity of Freund‐type adjuvant injected, the route of injection, and reaction at the depot site were studied for their roles in producing polyarthritis in rats. The intra‐dermal injection of Myobacterium butyricum in oil induced arthritis with much higher frequency than the subcutaneous or intravenous route. The minimal effective intradermal dose was 0.06 mg. M. butyricum in 0.02 ml. oil; 0.6 mg. mycobacteria in 0.1 ml. oil was required to produce polyarthritis in 100 per cent of rats. Wax fractions of mycobacteria did not induce arthritis. Neither a depot of adjuvant nor inflammation at the injection site was important as polyarthritis developed, even though amputation of the tail to remove the depot of injected adjuvant was performed within 2 hours after injection. While the mechanism of adjuvant‐induced polyarthritis remains unknown, the joint disease appeared dependent upon specific sites of dissemination of the adjuvant.