Overview of the Pulmonary Immune Response
The upper and lower airways together represent the largest epithelial surface exposed to the outside environment. The inspired air is a source of the necessary oxygen for the body, but also introduces numerous particles, toxic gases, and microorganisms inside the body. In addition, the lungs are inoculated repeatedly with bacteria which are aspirated from the nasooropharynx. In order to allow for gas exchange, foreign substances and microorganisms must be stopped and removed without undue in£ammation.