Experimental setup for collagen-induced arthritis. Female DBA/1 mice were ovariectomized (OVX) at 8 to 10 weeks of age and simultaneously received an implanted slow-release pellet containing 17β-estradiol (E2; 0.83 μg/day) or corresponding placebo. After 12 days of rest, they were immunized subcutaneously at the base of the tail with collagen type II and Freund’s adjuvant (day 0), which was repeated at day 21 or 28. Experiments were terminated at days 14, 23, 35 and 49 after the first immunization. Days 14 and 23 were considered as time points in the (asymptomatic) induction phase of collagen-induced arthritis (CIA), whereas days 35 and 49 were defined as established (symptomatic) CIA.