Host defense in respiratory infections

Pneumonia is a leading cause of morbidity and mortality. The host's system of defense against invading microbes is pivotal in prevention and in resolu tion of pneumonia after infection has been established. Anatomic and mechan ical barriers as well as innate immunity work to clear microorganisms that access the respiratory tract. After pathogens have secured a foothold, spec ific immune responses work to eliminate infection. Defects in any of the nu merous aspects of immune defense can predispose to infection with opportuni stic and more common organisms.