Silica decreases phagocytosis and bactericidal activity of both macrophages and neutrophils in vitro.

Silica, or silicon dioxide, has been shown to be toxic for macrophages. This is probably because it damages phagolysosomal membranes, allowing lysosomal enzymes to disrupt the cell. Neutrophils also take up particles such as silica and in addition they contain lysosomes. The purpose of this study was to determine whether incubation in vitro with silica inhibits function not only of mouse macrophages, but also of mouse neutrophils. The data show that incubation with silica for 1-3 hr decreases viability of both macrophages and neutrophils. Silica decreases the ability of macrophages and neutrophils to phagocytose both erythrocytes and bacteria, and it inhibits the ability of both cells populations to kill the facultative intracellular bacterium Listeria monocytogenes. Thus, it appears that silica, at least in vitro, is harmful to neutrophils as well as to macrophages.