Neutralizing Antibody Against Granulocyte/Macrophage Colony-Stimulating Factor Inhibits Inflammatory Response in Experimental Otitis Media

Objectives/Hypothesis: Granulocyte/macrophage colony-stimulating factor is important in the pathogenesis of acute and chronic inflammatory disease. We hypothesized that granulocyte/macrophage colony-stimulating factor plays a pivotal role in middle ear inflammation and that neutralization of granulocyte/macrophage colony-stimulating factor would inhibit neutrophil migration into the middle ear and production of inflammatory mediators. Study Design: Animal experiment. Methods: We used transtympanic administration of lipopolysaccharide, a major component of gram-negative bacteria, into mice to induce an experimental otitis media. Control mice received injection of phosphate-buffered saline into the middle ear cavity. Mice were systemically treated with granulocyte/macrophage colony-stimulating factor neutralizing antibody or control immunoglobulin G via intraperitoneal injection 2 hours before transtympanic injection of lipopolysaccharide or phosphate-buffered saline. Middle ear effusions were collected. Concentrations of interleukin (IL)-1 beta, tumor necrosis factor (TNF)-alpha, keratinocyte chemoattractant, and macrophage inflammatory protein-2 in middle ear effusions were measured by enzyme-linked immunosorbent assay. Histologic examination of the middle ear was also performed. Results: Transtympanic injection of lipopolysaccharide upregulated levels of granulocyte/macrophage colony-stimulating factor, IL-1 beta, TNF-alpha, keratinocyte chemoattractant, and macrophage inflammatory protein-2 in the middle ear. Concentrations of cytokines and chemokines were significantly decreased in mice injected with granulocyte/macrophage colony-stimulating factor neutralizing antibody. Infiltration of inflammatory cells into the middle ear cavity induced by lipopolysaccharide was also significantly reduced by neutralization of granulocyte/macrophage colony-stimulating factor. Conclusions: Systemic injection of granulocyte/macrophage colony-stimulating factor neutralizing antibody inhibits the middle ear inflammation induced by lipopolysaccharide in mice. Our findings suggest that granulocyte/macrophage colony-stimulating factor may offer a novel therapeutic target for the management of intractable otitis media.