NEUTROPHILS AND REACTIVE OXYGEN INTERMEDIATES MEDIATE GLUCAN-INDUCED PULMONARY GRANULOMA-FORMATION THROUGH THE LOCAL INDUCTION OF MONOCYTE CHEMOATTRACTANT PROTEIN-1

Monocyte chemoattractant protein-1 (MCP-1), which is required for full development of glucan-induced granulomas in the rat, is expressed in the walls of blood vessels at sites of glucan embolization. Early(1 ho ur) vessel wall expression of MCP-1 is temporally and anatomically lin ked to the transient accumulation of neutrophils, even though these ce lls are not present within definitive lesions. To ascertain the potent ial pathophysiologic role of neutrophils in glucan-induced granuloma f ormation, rats were neutrophil-depleted using specific antiserum. Ther e was a marked reduction in mean granuloma size and number in neutroph il-depleted animals when compared with neutrophil-sufficient controls. To determine potential mechanisms through which neutrophils may parti cipate in granuloma formation, the antioxidant enzymes superoxide dism utase and catalase were administered to neutrophil-sufficient animals that had received glucan. Superoxide dismutase treatment did not reduc e granuloma formation, whereas catalase treatment resulted in decrease d granuloma size, suggesting that H2O2 plays an important role in this process. The local expression of MCP-1 mRNA and protein, as determine d by in situ hybridization and immunohistochemical analysis, respectiv ely, was decreased in both neutrophil-depleted and catalase-treated an imals but not in superoxide dismutase-treated rats. Quiescent human um bilical vein endothelial cells incubated with either H2O2 or activated neutrophils secreted MCP-1. These data indicate that neutrophils and H2O2 are required for both full granuloma development and early blood vessel wall-associated MCP-1 expression after glucan infusion. These i n vivo data, coupled with in vitro data that indicate that both catala se-sensitive reagent H2O2 and neutrophil-derived reactive oxygen inter mediates (ie, H2O2) can induce MCP-1 secretion by human umbilical vein endothelial cells, support the hypothesis that neutrophils and neutro phil-derived products (H2O2) influence granuloma formation through ind uction of local MCP-1 expression.