Disease, Illness and Condition Library
Allergic Diseases of the Lungs The lungs are particularly vulnerable to allergic reactions because they are exposed to large amounts of airborne substances that often cause allergic reactions (called antigens), including dust, pollens, fungi, and chemicals. Exposure to irritating dusts or airborne substances, in many cases when a person is at work, may increase the chance of an allergic respiratory reaction. Allergic reactions involving the lungs may also occur from eating a particular food or taking a certain drug. The body’s natural reaction to an antigen is to form proteins that react with antigens (antibodies). Antibodies normally bind to an antigen (such as fungus), thereby rendering it harmless in an immune response. Occasionally, 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 grouped as type 1, 2, 3, or 4. Types of Allergic Diseases of the Lungs Hypersensitivity Pnuemonitis: Hypersensitivity pneumonitis (extrinsic allergic alveolitis, allergic interstitial pnuemonitis, and organic dust pneumoconiosis) is inflammation in and around the tiny air sacs (alveoli) and smallest airways (bronchioles) of the lung caused by an allergic reaction to inhaled organic dusts or, less commonly, chemicals. Causes: Many types of dust cause allergic reactions in the lungs. Organic dusts that contain microorganisms or proteins and chemicals, such as isocyanates, could cause hypersensitivity pneumonitis. Farmer’s lung, which is a result of repeated inhalation of heat loving (thermophilic) bacteria in moldy hay, is a well known example of hypersensitivity pneumonitis. Air conditioner lung is another example; this condition occurs when contaminated humidifiers or air conditioners (especially large systems in office buildings) circulate antigens that are capable of causing a hypersensitivity reaction. Only a small number of people who inhale these common dusts develop allergic reactions, and only a small percentage of those people who develop allergic reactions suffer irreversible damage to the lungs. Generally, a person must be exposed to large amounts of these antigens continuously or frequently over time before sensitivity and resultant disease develop. Lung damage appears to result from a combination of immune complex reactions and cell medicated allergic reactions. Initial exposures to the dusts sensitize lymphocytes. Some lymphocytes then help to produce antibodies that play a role in tissue damage. Other lymphocytes participate directly in inflammation after subsequent antigen exposure. Recurrent exposure to the antigen results in a chronic inflammatory response, which is manifested by a buildup of white blood cells in the walls of the alveoli and small airways. This buildup leads progressively to symptoms and disease. Continue Reading Eosinophilic Pneumonia: Eosinophilic pneumonia (also called pulmonary infiltrates with eosinophilia syndrome) is made up of a group of lung diseases in which eosinophils (a type of white blood cell) appear in increased numbers in the lungs and usually in the bloodstream. Eosinophils participate in the immune response of the lung. The number of eosinophils increases during many inflammatory and allergic reactions, including asthma, which frequently accompanies certain types of eosinophilic pneumonia. Unlike typical pneumonias caused by bacteria, viruses, and most often fungi, the tiny air sacs of the lungs (alveoli) are not infected in people with eosinophilic pneumonia. However, the alveoli and often the airways do fill with eosinophils. Even the blood vessel walls may be invaded by eosinophils, and the narrowed airways may become plugged with an accumulation of secretions (mucus) if asthma develops. The exact reason that eosinophils build up in the lungs is not well understood, and often it is not possible to identify the substance that is causing the allergic reaction. However, there are some know causes of esoinophilic pneumonia, including certain drugs (penicillin, aminosalicylic acid, carbamazepine, naproxen, isoniazid, nitrofurantoin, chlorpropamide, and sulfonamides [such as trimethoprimsulfamethoxazole]); chemical fumes (nickel inhaled as vapor); fungi (Aspergillus fumigatus); and parasites (roundworms, including nematodes). Continue Reading Allergic Bronchopulmonary Aspergillosis: Allergic bronchopulmonary aspergillosis is an allergic lung disorder that often mimics pneumonia and is characterized by asthma, airway and lung inflammation with eosinophils (a type of white blood cell), and increased numbers of eosinophils in the blood. Allergic bronchopulmonary aspergillosis is caused by an allergic reaction to a fungus, most commonly Aspergillus funigatus. This fungus thrives in soil, decaying vegetation, foods dusts, and water. A person who inhales the fungus may become sensitized and develop allergic asthma. Other fungi, inclugin Penicillium, Candida, Curvularia, and Helminthosporium, can cause an identical illness. In some people, a more complex allergic reaction can develop in the airways and lungs. The disorder differs from typical pneumonias caused by bacteria, viruses, and most fungi, in that the fungus does not actually invade the lungs or directly destroy tissue. The fungus does colonize the asthmatic mucus in the airways and causes recurrent allergic inflammation in the lungs. The tiny air sacs of the lungs (alveoli) become packed primarily with eosinophils. Increased numbers of mucus producing cells may also appear. In advanced cases, inflammation may cause the central airways to widen permanently, a condition called bronchiectasis. Over time the lungs are likely to become scarred. Other forms of aspergillosis can occur. Aspergillus can invade the lungs and cause serious pneumonia in people with an impaired immune system. This condition is an infection, not an allergic reaction. The fungus can also form a fungus ball, called an aspergilloma, in cavities and cysts of lungs already damaged by another disease, such as tuberculosis. The major consequence of such fungus balls is lung bleeding, often severe, which becomes evident when the person coughs up blood and is short of breath. Continue Reading
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