Respiratory tract infections: intrinsic risk factors

A complex system exists to provide defense of the respiratory tract against infection. The three major components of the respiratory defense system are mechanical (such as cough and mucociliary clearance), humoral (such as secretory immunoglobulins and complement), and cellular (such as alveolar macrophages, lymphocytes, and neutrophils). These components are important in both upper as well as lower airways, but their relative importance varies according to location. Along with an increased understanding of the mechanisms for respiratory host defense has been the demonstration of numerous intrinsic defects in this system. Increased frequency of respiratory infections has clearly been associated with intrinsic defects. These associations will be described.