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 resolution of pneumonia after infection has been established. Anatomic and mechanical barriers as well as innate immunity work to clear microorganisms that access the respiratory tract. After pathogens have secured a foothold, specific immune responses work to eliminate infection. Defects in any of the numerous aspects of immune defense can predispose to infection with opportunistic and more common organisms.