Response of the lung to inhaled antigens

Bird Fancier's lung: An underdiagnosed etiology of dyspnea

Bird Fancier's Lung is a type of hypersensitivity pneumonitis, an immunologically mediated lung disease due to repetitive exposure of air-borne avian antigen. This was first described in 1965 and is known as one of the most common causes of hypersensitivity pneumonitis. This case highlights this underdiagnosed etiology of dyspnea, disease presentation and exposure variability, and methods of diagnosis.

Respiratory Allergic Disorders

Allergic asthma refers to a chronic reversible bronchoconstriction influenced by an allergic trigger, leading to symptoms of cough, wheezing, shortness of breath, and chest tightness. Allergic bronchopulmonary aspergillosis is a complex hypersensitivity reaction, often in patients with asthma or cystic fibrosis, occurring when bronchi become colonized by Aspergillus species. The clinical picture is dominated by asthma complicated by recurrent episodes of bronchial obstruction, fever, malaise, mucus production, and peripheral blood eosinophilia. Hypersensitivity pneumonitis is a syndrome associated with lung inflammation from the inhalation of airborne antigens, such as molds and dust.

Hypersensitivity pneumonitis: beyond classic occupational disease-changing concepts of diagnosis and management

OBJECTIVE

To review inhaled antigens in home environments that cause hypersensitivity pneumonitis (HP) of varied clinical expressions and histopathologic patterns.

DATA SOURCES

Computer-assisted MEDLINE and manual searches for articles concerning HP, interstitial lung disease (ILD), epidemiology of HP and ILD, challenge procedures of HP, and indoor fungi.

STUDY SELECTION

Published articles concerning inhaled antigens in home environments and HP were selected.

RESULTS

Current criteria for the diagnosis of HP are too restrictive, because most apply only to the classic acute presentation and are of limited value in the subacute and insidious forms. Clinical expressions vary across the gamut of respiratory tract signs and symptoms. Patterns on lung biopsy may include all histopathologic descriptions of idiopathic ILD. The home is the likely causative environment rather than the workplace. Exposures may be occult and require in-depth environmental histories and on-site investigations to detect antigens and sources.

CONCLUSIONS

Natural or environmental challenges have become an important tool for diagnosing HP and determining effectiveness of remediation. Early diagnosis and effective remediation of the cause lead to a high survival rate, whereas diagnosis in advanced stages leads to disability and/or premature death.

Cytokines, platelet activating factor and eosinophils in asthma

Understanding of the pathogenesis of asthma has increased considerably during the past few years. These advances were possible through scientific progress in three areas which contribute to this complex and multifaceted disease: (a) the much clearer understanding of eosinophil function; (b) the defining of lipid mediators in tissue inflammation and bronchial obstruction; and (c) the growing knowledge about the biological action of a new class of protein hormones, collectively called cytokines. In line with this, evidence has accumulated of how these components may interact with each other in providing the basis of inflammatory processes in asthma. Hence it seems appropriate to review the potential implications of this new information for the pathogenesis and therapy of this disease.

Hypersensitivity pneumonitis

Hypersensitivity pneumonitis or extrinsic allergic alveolitis is an immunologically mediated lung disease caused by repeated inhalations of organic antigens. The basic histologic lesion consists of a diffuse mononuclear cell infiltration of alveolar wall, alveoli, terminal bronchioles, and neighboring interstitium. The inflammation is often followed by granulomas, which then may progress to fibrosis. Although there is no single radiologic, physiologic, or immunologic test specific for hypersensitivity pneumonitis, the diagnosis can often be suspected on the basis of a compatible temporal relationship of pulmonary symptoms to the history of environmental or occupational exposure. Once the diagnosis is suspected, the presence of serum precipitating antibodies (IgG), suppressor cytotoxic lymphocytosis in bronchoalveolar lavage fluid, and granulomatous alveolitis in lung biopsy specimens are extremely helpful in confirming the diagnosis. In patients where the diagnosis is confirmed, avoidance of the causative antigen is the best therapy, although corticosteroids are used to suppress inflammation. Once the fibrosis is set in, the patient may gradually slide into respiratory failure, cor pulmonale, and death.

The role of eosinophils in asthma

During recent years it has become apparent that the eosinophil may represent a powerful effector cell in the pathogenesis of asthma, particularly in the late asthmatic response. It can be stimulated by a number of stimuli among which PAF appears to be one of the most effective. The eosinophil is a source for a variety of proinflammatory and toxic products with profound effect in the lungs and airways. These eosinophil products mimic some of the features of asthma and the strong association of the eosinophil with asthma has led to the suggestion that asthma would be better classified as "chronic desquamating eosinophilic bronchitis." Although the evidence known to date is persuasive many questions still remain unanswered and await further investigation. Future therapeutic approaches in asthma may aim at interrupting the mechanisms leading to eosinophil bronchial accumulation and activation.

The inflammatory theory of asthma

In summary, these observations suggest a model for asthma which is summarized in Table III. Initially, mast cells and possibly other bronchial cells, e.g., alveolar macrophages, are activated either in an IgE-dependent or, in intrinsic asthma, in an IgE-independent fashion. These cells release two sets of mediators which may be either preformed or newly synthesized. One set of mediators is responsible for the immediate bronchospastic response. This bronchospasm is transient, readily reversible, and not associated with either airway inflammation or bronchial hyperreactivity. The second set of mediators, however, promote chemotaxis and activation of neutrophils and eosinophils. The subsequent bronchial inflammation causes damage and desquamation of the respiratory epithelium. The increased exposure of irritant receptors results in hyperreactive airways. In addition, these inflammatory cells induce mast cell degranulation and recurrent bronchospasm. Thus, after the initial exposure to allergen, a vicious cycle of inflammation, hyperreactivity and recurrent mast cell degranulation develops, ultimately leading to the pathological picture of chronic asthma.

Role of inflammation and inflammatory mediators in airways disease

Recent evidence suggests that airway inflammation is linked to hyper-responsiveness of airway smooth muscle. Increases in airway responsiveness after many stimuli are accompanied by increases in inflammatory cells in bronchoalveolar lavage fluid and in the airway epithelium. Airway epithelial cells may themselves be an important source of inflammatory mediators, producing metabolites that can cause chemotaxis of neutrophils and that can selectively activate other cells in the lungs. Mast cells produce a variety of enzymes and vasoactive, chemotactic, and bronchoconstrictor substances in response to non-immunologic as well as immunologic stimuli. The secretory profile of a mast cell may depend upon the specific stimulus applied. In addition, different populations of mast cells exist and distinct enzymatic pathways may predominate in different cell types. Mediators released by these cells may activate target cells by direct or indirect mechanisms. These inflammatory mediators, together with inflammatory cells, are important in the complex interactions involving airway epithelial cells, neutrophils, mast cells, smooth muscle, respiratory secretory cells, and nerves, which, in concert, are responsible for the pathophysiologic manifestations of obstructive lung disease.

Significance of IgG antibodies against environmental microbial antigens in a farming population

A group of dairy farmers studied 6 years earlier in a field survey was re-surveyed for respiratory symptoms, occupational capability and the presence of antibodies against environmental micro-organisms. Specific IgG antibodies to Micropolyspora faeni, Thermoactinomyces vulgaris, Aspergillus umbrosus and Aspergillus fumigatus were measured by ELISA from the serum samples obtained in the two surveys. Antibody titres remained constant in 70% of both farmers and controls, but where changes took place, the titres against the actinomycete antigens tended to rise, whereas both increases and decreases were detected equally against the Aspergillus antigens. The titre of specific antibody to any of the four micro-organisms, when measured from a single serum specimen, seemed to be of little diagnostic value. Observed changes however, were more diagnostic, in that a fall in titre, especially against the Aspergillus antigens, was closely associated with a definite decrease in exposure, such as after retirement. Increased titres occurred in farmers with continued exposure, and those against the actinomycetes were associated with the appearance of symptoms in previously symptom-free individuals. In a case of farmer's lung which developed in this population during the follow-up period, significant increases were detectable against T. vulgaris and M. faeni.

Usefulness of skin test in Farmer's lung

The skin test with hay extract or with Micropolyspora faeni (MF), is not commonly used in the diagnosis of Farmer's lung (FL), as it is not considered specific. In our study, we have applied the intracutaneous test with these antigens in 26 patients affected with FL; 18 of them were still in contact with the antigen and the remaining eight had not been in contact with the hay during the previous year. Twenty-five asymptomatic farmers (AF) served as a control group. In the first group and with hay extract, the immediate reading (I) was positive in 15 of 18 (83.3 percent), the late reaction (L) in 18 of 18 (100 percent), and the delayed one (D) in eight of 18 (44.4 percent). In the 25 AF, the results were as follows: I, seven of 85 (28 percent); L, 17 of 25 (68 percent); and D, one of 25 (4 percent). Consequently, the differences between both groups were significant: I, p less than 0.01; L, p less than 0.05; and D, p less than 0.01. Using MF as an antigen, the test is somewhat less effective: p less than 0.02, p less than 0.02, and p less than 0.2, respectively. These results suggest that the intradermal injection with hay extract is an easy, effective test in the diagnosis of FL, and at the same time, a better means of distinguishing FL patients from AF than the precipitation test.

Role of histamine in the aetiology of byssinosis. I Blood histamine concentrations in workers exposed to cotton and flax dusts

The formation or the accumulation, or both, of histamine in the lungs may be potentiated by agent(s) present in cotton dust at higher level(s) than in flax dust and negligible in cottonseed dust. It has been suggested that such potentiation may be due to the activation of the ability of the lung to produce histamine and/or produce or recruit mast cells; this may present an acceptable explanation of the mechanism by which the propagation of the chronic effect of the dust proceeds in cotton and flax workers. Histamine accumulated in the lung over the weekend is released on exposure to dust causing the symptoms of byssinosis. The difference in the rate of histamine metabolism relative to the rate of histamine formation in byssinotic subjects leads to a more prolonged histamine accumulation than in symptom free subjects, with the consequent appearance of the symptoms of byssinosis. Continuous exposure to dust, without weekend interruption, leads to equivalent rates of histamine formation and metabolism with non-considerable histamine accumulation in the lungs and consequent absence of the symptoms of byssinosis.

Cadmium induced metal fume fever: results of inhalation challenge

Inhalation challenges were performed on a patient who had developed symptoms of metal fume fever, after six years of welding. Vital signs, white blood cell count and differential, nasal smears, chest X-ray, and pulmonary function tests were monitored during each inhalation challenge. There was no significant reaction to methylcholine, or to fumes of zinc, copper, and mild steel. Significant restrictive ventilatory impairment, leucocytosis, fever, and symptoms of metal fume fever were noticed after exposure to fumes of silver solder containing twenty four percent cadmium.

Evaluation of the patient for occupational immunologic lung disease

Careful evaluation of the worker patient is essential to detect occupational immunologic disease (OILD) and to define the source of the illness. The history is essential, especially in view of the temporal relationships between symptoms and exposure: the presence of variable latent periods between exposure and symptoms must be considered. Once OILD is suspected, additional evaluation is of value. Physical examination may be normal or may detect features of asthma or interstitial disease, depending on the stage of the illness. Chest x-ray evaluation may also reflect the type and stage of illness. Serologic studies may detect precipitating antibodies against environmental antigens. Skin tests with common antigens are useful in detecting an atopic background. Environmental studies may reveal particular antigens in the form of fungi, thermophilic actinomycetes, or chemicals that are volatile, soluble, or could be aerosolized. Pulmonary function studies before and after the work shift or after a period of avoidance may provide clues as to the environmental nature of the illness. Bronchopulmonary challenge with occupational environmental materials may be valuable in obtaining a definitive diagnosis. Therapy of OILD depends on the worker's response, degree of illness, and feasibility of avoidance of protection.

Baker's asthma (grain-dust-induced asthma)

A 48-year-old black male with no underlying atopy developed asthma after working nine years at a bakery. The attacks of wheezing were preceded by nasal symptoms and usually occurred after several hours of work. Skin testing revealed reactivity to dust, molds, and wheat extracts; serum level of IgE was normal, and a RAST screen to common allergens was negative. A bronchial provocation test using commercial wheat extract was negative, but the same test using the patient's own bakery flour resulted in an immediate positive reaction. The pathogenesis and management of grain-dust-induced asthma are discussed.

Antigen-specific densensitization in a rabbit model of acute hypersensitivity pneumonitis

Rabbits that had been prepared to develop acute alveolitis after aerosol challenge with simple protein antigens did not develop chronic alveolitis but rather gradually recovered despite continued challenge. Immunologic accompaniments of waning disease were compared in this model to those associated with intravenous injections of antigen causing "desensitization." We also studied the effects of aerosol challenge prior to systemic immunization, antigen specificity, and the duration of desensitization by aerosolized and intravenous antigen. We found that repeated aerosol or intravenous challenges produced antigen-specific desensitization in this model, and the effect lasted several weeks. Prior exposure to aerosolized antigen was not protective. Neither aerosol nor intravenous desensitization maneuvers abrogated antigen-specific lymphocyte blastogenesis, although an early transient fall did occur. Humoral responses were boosted. These findings suggest that chronic alveolitis is prevented in this model by specific desensitization, without the induction of true tolerance or of nonspecific anergy. Such immunoregulation may result from development of antigen-specific blockade or blocking factors (e.g., lymphokines), antigen-antibody complexes, or suppressor cells affecting specific effector cells. Evaluation of these mechanisms may have implications for diagnosis and prognosis in human hypersensitivity pneumonitis.

Enzyme-linked immunosorbent assay (ELISA) for IgG antibodies in farmers' lung disease

The ELISA was used for detection of specific IgG antibodies to Micropolyspora faeni antigens in 158 farmers with a history of exposure to mouldy hay, eighty-eight of whom had a diagnosis of farmer's lung. The farmers' lung group had significantly higher values in the ELISA than both the seventy exposed but asymptomatic farmers (P less than 0.001) and a group of thirty-one adult controls (P less than 0.001). The asymptomatic farmers also had significantly higher values than the control group (P less than 0.02). The ELISA correlated better with the clinical diagnosis than the Ouchterlony agar-gel double-diffusion (precipitin) test. None of the control group gave positive reactions in the ELISA or the precipitin tests. The ELISA is therefore a sensitive, specific and quantitative test which is readily available and widely applicable.

Case report: metal fumes fever

A young male foundry worker had headache, nonproductive cough, orthopnea, formication, rigor, fever, and substernal pain after exposure to concentrated metal fumes. Examination revealed bilateral basal rales. Serial spirometry suggested a transitory restrictive impairment with persistent mild to moderate obstructive impairment. Leukocytosis, hypoxemia, and the other symptoms resolved with no therapy other than the patient's removal from the polluted area.

Injury and repair of the lung: response to intravenous Freund's adjuvant

Tissue from the lungs of rabbits was examined at intervals up to 24 weeks after the animals had received a single intravenous injection of Freund's complete adjuvant. Though this is not a conventional method for damaging the peripheral lung, it had the advantage of producing multiple lesions in which most tissue components were altered for a prolonged period. White blood cells were present within the tissue and air spaces of these damaged areas. They persisted for 6 weeks in large numbers and gradually decreased over the next 12 weeks. There was replacement of type A by type B alveolar lining cells. Basement membranes were displaced and lost. Elastic and collagen fibres were distorted and destroyed. Blood vessels were occluded. Epithelioid cell and foreign body granulomas developed. Interalveolar septa disappeared, and air spaces were compressed. Despite all these changes the lungs regained near normal structure by 24 weeks after the initial injury. These results do not support the importance that has been placed on damage to various structural components of the lung as an explanation for chronic pulmonary disease. They do give some insight into the capacity of peripheral lung tissue for regenerationa following a single injury that induces a prolonged inflammatory response.

Early detection of hypersensitivity pneumonitis in office workers

Symptoms of hypersensitivity pneumonitis in three employees in an office building led to an investigation of their work environment. An open spray water air cooling system was implicated when inhalation challenge with the spray water caused acute illness in one of them. A questionnaire survey of the 4,023 co-workers identified 48 other suspect cases, and laboaratory studies confirmed hypersensitivity pneumonitis in three additional workers of this group. A significant change in pulmonary function, occurring only after exposure to the work environment, was the most useful laboratory finding and was found in five workers with no other pulmonary abnormalities, but not is asymptomatic workers or controls, since five of the six patients with hypersensitivy pneumonitis worked in offices cooled by the spray water system and since three had positive responses to inhalation challenge, use of the spray water system was discontinued. The affected workers improved after they were removed from the office complex.

Pulmonary hypersensitivity to Alternaria and Aspergillus in baker's asthma

In two cases of baker's asthma pulmonary hypersensitivity was found to the fungi Alternaria and Aspergillus. Provocative bronchial challenge revealed a dual response; an immediate and an Arthus type hypersensitivity to Aspergillus in the first case. A primary binding assay revealed high titres of anti-Aspergillus antibody in the serum. In the second case intradermal and bronchial challenge suggested an immediate type I hypersensitivity response to Alternaria. The suspected organisms were present in the room air of the bakeries. It is suggested that an immunological response to these airborne fungi may have contributed to the pathogenesis of baker's asthma.

The role of immune complexes in the pathogenesis of disease

Circulating antigen-antibody complexes are incriminated in the pathogenesis of auto-immune and inflammatory disease, and more recently malignancy. Extensive knowledge of the immunopathological reactions has evolved from from the study of experimental serum sickness in animals and of the potential aetiological agents (e.g. viruses) from spontaneous immune complex diseases in animals. Numerous techniques, both direct and indirect, have now been described to identify immune complexes in serum, though no single technique will identify regularly immune complexes in all clinical situations, nor will it demonstrate the pathogenicity of the immune complex in a given patient. Human disorders with a definite immune complex basis (glomerulonephritis, systemic lupus erythematosus, rheumatoid arthritis) and others with a possible immune complex basis (e.g. cutaneous vasculitis, are presented. Management of immune complex disorders is based on removal of the initiating agent if known (e.g. infection, drug, malignancy) or the use of non-specific anti-inflammatory therapy. Specific immunotherapy, in practice and theory, is discussed.