Superoxide anion generation by human neutrophils exposed to monosodium urate.

We studied the capacities of naked and protein-coated monosodium urate (MSU) crystals to stimulate superoxide anion (O(2)) release by human polymorphonuclear leukocytes (PMN). Uncoated MSU estimated significant O(2) production by cytochalasin B-treated PMN. Precoating MSU with IgG caused an increase in mean O(2) production, whereas precoating heated MSU with serum or plasma inhibited O(2) release. Unheated MSU crystals, which activate complement to a greater extent than heated crystals, also provoked O(2) generation, an effect again abrogated by precoating with serum but not with plasma. Coincubation of unheated MSU and plasma resulted in an enhancement of O(2) generation. The results of these experiments support the hypothesis that adsorbed proteins modulate the phlogistic potential of MSU and that the surface activation of humoral mediators contributes to the local inflammatory response.