Protective reflex of the tracheo-bronchial tree that restricts entry of potentially damaging substances into the deeper and more vulnerable parts of the respiratory system. Subepithelial irritant receptors are stimulated by inhaled noxious gases, particulate matter, allergens, or pathogens. The motor response resulting from the stimulation results in rapid bronchospasm, glandular secretion, and histamine release. This can also occur during bronchoscopic procedures. SYN: irritant reflex.