Aggravation of adjuvant arthritis by carrageenan.

1. We have studied the optimum conditions for the induction of adjuvant carrageenan-induced inflammation (ACII) in male Wistar rats with limited susceptibility to adjuvant arthritis (AA). 2. ACII was induced by intradermal injection of Freund's complete adjuvant (CFA), containing 10 mg/ml Mycobacterium tuberculosis, followed by a subplantar inoculation of the nonspecific inflammatory stimulus carrageenan at different times. 3. Data obtained indicate that the arthritis of rats inoculated with CFA is significantly increased by carrageenan, particularly when it is injected 14 days after the adjuvant. Arthritis enhancement was more evident in the joints of the leg that had been previously injected with carrageenan, and remained stable around the peak level for some weeks. The development of joint inflammation was associated histologically with the appearance of inflammatory cells in the synovial membrane of those animals. 4. We found that the injection of carrageenan aggravated the course of AA in general, but very significantly when administered at the moment of the appearance of arthritis (day + 14). This aggravation affected both the intensity of inflammation and the chronicity of the disease.