ENDOTOXIN RESPONSIVENESS AND GRAIN DUST-INDUCED INFLAMMATION IN THE LOWER RESPIRATORY-TRACT

To identify the role of endotoxin responsiveness in grain dust-induced airway disease, we used two models of extotoxin hyporesponsiveness to perform inhalation exposure studies in mice. In the first model, we investigated whether genetic resistance to endotoxin would alter the inflammatory response to inhaled grain dust by comparing the inflammatory response in the lower respiratory tract of endotoxin-sensitive and -resistant male mice after inhalation of pyrogen-free saline, corn dust extract (CDE), sterile CDE (SCDE), or lipopolysaccharide (LPS). Endotoxin-sensitive and -resistant mice were exposed for 4 h to nebulized solutions of LIPS, SCDE, or CDE. Another group of endotoxin-sensitive and -resistant mice was sham exposed for 4 h to nebulized sterile saline. Dose-response relationships for endotoxin were explored for LPS, SCDE, and CDE. Bronchoalveolar lavage (BAL) 5 h after the start of exposure demonstrated a higher concentration of total cells, neutrophils (PMNs), and tumor necrosis factor-alpha (TNF-alpha) in BAL fluid after inhalation of CDE, SCDE, or LPS in endotoxin-sensitive than in endotoxin-resistant mice. Whereas endotoxin-sensitive mice demonstrated a dose-response relationship between the endotoxin concentration in each of the solutions and the concentration of cells, PMNs, and TNF-alpha in BAL fluid, concentrations of TNF-alpha were significantly higher only in BAL fluid of endotoxin-resistant mice exposed to higher concentrations of SCDE or CDE. In the second model, we investigated whether acquired endotoxin tolerance would alter the inflammatory response to SCDE. Endotoxin-sensitive mice were injected daily for 4 days with increasing doses of LPS to induce tolerance or with sterile saline. On day 5, mice were exposed to nebulized LPS or SCDE for 4 h. Sensitive mice preexposed to LPS demonstrated a significantly reduced concentration of total cells, PMNs, and TNF-alpha compared with controls for inhaled LPS and SCDE. Each of the measures of inflammation was reduced by greater than or equal to 50% compared with control mice. These results demonstrate that responsiveness to endotoxin is critical to development of grain dust-induced inflammation in the lower respiratory tract and support our hypothesis that endotoxin may be the principal mediator of the acute inflammatory response to inhaled grain dust.