Introduction

The lungs are particularly prone to allergic reactions because they are exposed to large quantities of airborne substances that commonly cause allergic reactions (called antigens), including dusts, pollens, fungi, and chemicals. Exposure to irritating dusts or airborne substances, often when a person is at work, may increase the likelihood of an allergic respiratory reaction. Allergic reactions involving the lungs may also occur from eating a certain food or taking a certain drug.

The body reacts to an antigen by forming proteins that react with antigens (antibodies). Antibodies typically bind to an antigen (such as a fungus), thereby rendering it harmless in an immune response (see Section 16, Chapter 183). Sometimes, however, when the antibody and antigen interact, inflammation and tissue damage occur; this is called an allergic reaction. Allergic reactions are classified by the mechanisms that are involved in causing the tissue damage. Many allergic reactions involve a combination of more than one type of tissue damage. Some allergic reactions depend on antigen-specific lymphocytes (a type of white blood cell) rather than on antibodies. Reactions are typically categorized as type I, II, III, or IV.