Priming activity of supernatants from monosodium urate (MSU) crystal-stimulated monocytes (SMMs) on chemiluminescence (CL) production by neutrophils. Monocytes were incubated for 18 hours with MSU crystals (1 mg/mL) with or without alpha-melanocyte-stimulating hormone (α-MSH) (10-6 M) or (CKPV)2 (10-6 M). The cell-free supernatants were used to pretreat purified neutrophils (30 minutes at 37°C) before analysis of their CL production in response to MSU (3 mg/mL). Results are expressed as peak CL values in millivolts. Bars denote mean ± standard error of the mean. °P < 0.001 versus RPMI; *P < 0.05 and **P < 0.01 versus SMMs.