Outline of the air pouch experiments. (a) Sequence of events. Air is injected subcutaneously on day 0 and again on day 3 to keep the pouch inflated. On day 6 the remaining air is aspirated, and the monosodium urate (MSU) crystal suspension (2 mg in 1 ml phosphate-buffered saline [PBS]) or 1 ml PBS only is injected into the pouch cavity. Pouch exudate and tissue are obtained for analysis up to 50 hours after crystal injection. (b) Determination of the time of maximal inflammation in the pouch lumen. MSU crystal suspension (2 mg in 1 ml PBS) was injected into the pouch at t = 0 hours. Pouch exudate leukocyte counts were determined by manual cell counting at the indicated time points (n = 4 mice for each time point).