Chemotactic properties of supernatants from monosodium urate (MSU) crystal-stimulated monocytes (SMMs). 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) or polymyxin B (10 μg/mL). The cell-free supernatants from 10 separate experiments (two with polymyxin B) were used as chemoattractants for purified human neutrophils. In three separate experiments, SMMs were preincubated (15 minutes at room temperature) with anti-interleukin-1 (anti-IL-1) or anti-IL-8 monoclonal antibodies or both before use as chemoattractants. The chemotactic activity of the standard chemoattractant N-formyl-methionyl-leucyl-phenylalanine (FMLP) (10-8 M) is shown. Results are expressed as number of neutrophils per high-power field (hpf). Bars denote mean ± standard error of the mean. *P < 0.05; **P < 0.01; ***P < 0.005 versus SMMs.