Female Lewis rats weighing ~100 g (Janvier Laboratories, Saint-Germain-sur-l’Arbresle, France), were injected subcutaneously at the base of the tail with 300 µl (5 mg ml−1) of lyophilized Mycobacterium butyricum (Difco Laboratories, Detroit, MI), as previously described26. In this model, the first signs of joint inflammation and pain appear after day-8 of induction and become maximal during days 14–1826.