Chest
Volume 75, Issue 2, February 1979, Pages 270-274
Journal home page for Chest

Hypersensitivity Pneumonitis
Hypersensitivity Pneumonitis; State of the Art

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Etiologic Agents

A large number of occupational, avocational and iatrogenic sources of antigen are being recognized continuously. These include antigens derived from microorganisms (bacteria, fungi, Actinomycetes and amoebae), animal protein, and plant protein. Certain small molecular weight chemicals and drugs may also produce the disease. It has been well established that the antigenic load of these substances is heavy. For example, it has been estimated that a farmer, working in an environment where aliquots

Clinical Features

There have been some recent new insights into the clinical presentation of these diseases and it is becoming increasingly apparent that the intensity and frequency of exposure to etiologic antigens determines the clinical categories of acute and chronic forms of the disease. The importance of obtaining a careful occupational history remains paramount in diagnosis, as is the realization that the classic symptoms of cough, fever, chills, malaise and dyspnea are often mistaken for a bacterial or

Diagnosis

The first diagnostic step is to establish an association between inhalation exposure to an organic dust or animal protein and the development of pneumonitis symptoms. Although immunologic laboratory procedures may be additionally useful in establishing a specific diagnosis, many of these are unfortunately still limited to the academic environment because of the technology required. Even when such tests are performed with proper controls, they do not always differentiate between individuals with

Pathology

Although there have been several recent exciting immunofluorescent and histopathologic findings in the idiopathic fibrotic pulmonary diseases, immunofluorescent studies in hypersensitivity pneumonitis continue to be generally unrewarding. Most varieties of the disease are characterized by similar histologic changes which largely depend upon the intensity of antigenic exposure and the stage of the disease at the time of biopsy. The basic tissue reaction consists of alveolar and interstitial

Pathogenesis

The most intriguing recent studies of the disease have been in the area of pathogenesis. The antigens involved have been shown to exert several important biologic effects including the following: nonspecific activation of serum proteins (complement alternate pathway) and cells (alveolar macrophages); immune response enhancement (a nonspecific adjuvant effect); a specific humoral and cellular immune response (serum antibody and lymphokine production); and tissue destruction (macrophage lysosomal

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