 studies have implicated active oxygen species ( aos ) in the pathogenesis of various lung diseases . 
 many chemical and physical agents in the environment are potent generators of aos , including ozone , hyperoxia , mineral dusts , paraquat , etc . 
 these agents produce aos by different mechanisms , but frequently the lung is the primary target of toxicity , and exposure results in damage to lung tissue to varying degrees . the lung has developed defenses to aos - mediated damage , which include antioxidant enzymes , the superoxide dismutases [ copper - zinc ( cuznsod ) and manganese - containing ( mnsod ) ] , catalase , and glutathione peroxidase ( gpx ) . in this review , 
 antioxidant defenses to environmental stresses in the lung as well as in isolated pulmonary cells following exposure to a number of different oxidants , are summarized . 
 each oxidant appears to induce a different pattern of antioxidant enzyme response in the lung , although some common trends , i.e. , induction of mnsod following oxidants inducing inflammation or pulmonary fibrosis , in responses to oxidants occur . 
 responses may vary between the different cell types in the lung as a function of cell - cycle or other factors . 
 increases in mnsod mrna or immunoreactive protein in response to certain oxidants may serve as a biomarker of aos - mediated damage in the lung.imagesfigure 3 . 
Images