Modulation of human neutrophil and monocyte oxidative burst byLegionella pneumophila sonic extract

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Abstract
The effect of Legionella pneumophila sonic extract on human neutrophil and monocyte oxidative burst was studied by Superoxide anion release and luminol-enhanced chemiluminescence assays.Legionella pneumophila sonic extract by itself did not stimulate neutrophils and monocytes. The sonic extract at 8–2000μg/ml primed neutrophils for enhanced Superoxide release and, at 8–62.5 μg/ml, for enhanced chemiluminescence. Monocytes were only primed for enhanced chemiluminescence at very low extract concentrations (below 16μg/ml). Monocyte Superoxide release was suppressed by extract concentrations higher than 2000μg/ml and the chemiluminescence response of neutrophils and monocytes by concentrations higher than 250 and 125 μg/ml, respectively. The priming activity was heat stable and present in fractions below 5 kDa. On the basis of these findings it is suggested that enhanced production of oxygen metabolites by neutrophils in contact with legionella components at low concentrations could contribute to the lung tissue damage seen in Legionnaires' disease, whereas the suppression of phagocyte oxidative burst by higher extract concentrations may be one of the mechanisms by which Legionella pneumophila survives intracellularly.

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