Time course of endotoxin-induced airways' inflammation in healthy subjects

Few data are available on the kinetic of the airways' inflammation induced by inhaled endotoxin in a given subject. The purpose of this study was to evaluate in healthy subjects the time-related endotoxin-induced airways' inflammation. The cells counts from the induced-sputum were evaluated before, 6 and 24 h, and 7 days after an exposure to 20 mcg inhaled endotoxin, in eight pre-selected volunteers. To avoid interference of the induced-sputum procedure on the response to endotoxin, each time-point was evaluated in randomized order at 2-weeks interval after three separate inhalations of endotoxin. A significant rise of the relative number of lymphocytes (p<0.05) and polymorphonuclear neutrophils (PMN; p<0.02) and of the absolute number of PMN (p<0.05) occurring at 6 h, followed by an increase of the absolute number of the total viable cells (p<0.01), macrophages (p<0.001), neutrophils (p<0.01), and lymphocytes (p<0.05) at 24 h after endotoxin inhalation. The inflammatory response recovered totally after 7 days. In human beings, the inhalation of endotoxin induced a transient airway inflammation after 6 h, peaked at 24 h and recovered after 7 days. When repeated endotoxin inhalations are used as a model of inflammation, a wash-out period of at least 7 days should be applied between each exposure in each subject.