Modulation of host defenses by exposure to oxidant air pollutants

This report reviews the literature on modulation of host defenses by oxidant air pollution, and possible links with increased susceptibility to respiratory infections. The notion of increased susceptibility to respiratory infections is primarily based on available animal data. Since the basic biological mechanisms of action of the human and the animal pulmonary defenses are similar, it is reasonable to extrapolate these biologic responses in experimental animals to human exposures. However, no firm conclusions on a relationship of exposure to oxidant air pollutants and defense to infections can yet be drawn from epidemiologic data. At this point it is not possible to answer questions such as the relative importance of duration and concentration of exposure, and reversibility and adaptation phenomena, although these issues are of the utmost importance for population risk assessment. Research at various levels is required to fill the scientific gaps. Experimental inhalation toxicologic research using human volunteers and laboratory animals should focus on dose and time-course dependence, mechanisms of effects of exposure to oxidant gases, and the extent of reversibility of the effects. Epidemiologic studies on prevalence and nature of respiratory infections and possible association with exposure to air pollutants are also needed.