Cellular immune response to fractionated avian antigens by peripheral blood mononuclear cells from patients with pigeon breeder's disease

Pigeon breeder's disease (PBD), a form of hypersensitivity pneumonitis caused by repeated inhalation of antigens of pigeon origin, is characterized by a diffuse inflammation of the lower respiratory tract. Although a variety of immunologic and nonimmunologic mechanisms have been described in the development of the disease, the pathogenesis is still far from clear. In this study we analyzed the T-lymphocyte proliferative response to a variety of avian antigens with use of peripheral blood mononuclear cells from 11 patients who had PBD and 10 healthy volunteers. We used a new method based on avian antigen-bearing nitrocellulose particles derived from Western blots to study the T-cell proliferative response to 15 antigenic fractions obtained from pigeon serum. With this technique, complex mixtures of antigens can be fractionated by polyacrylamide gel electrophoresis, transferred to nitrocellulose membranes, and used for T-cell proliferation assays with selected antigenic determinants. A wide variety of responses were observed, and there were no reproducible patterns of reaction within either group. Nine of 10 healthy subjects responded to some soluble fractions. However, patients with PBD displayed the strongest response and responded to a significantly greater number of antigenic fractions. Fraction 2, representing a 220 kd molecular weight protein, was the only immunodominant antigen when both groups were compared; it was recognized by 73% of the patients with PBD and by only 20% of control subjects (p < 0.03). These findings show that T lymphocytes of patients with PBD recognize a wide range of bird proteins, which induce marked T-cell proliferation.

Detection of salivary and seric IgG and IgA antipooled pigeon sera activities in patients with pigeon breeder's disease

Pigeon breeder's disease (PBD) is an interstitial lung disease induced by exposure to pigeon antigens. Search of antipigeon antigen antibodies (APSA) in serum or bronchoalveolar lavage is generally used for auxiliary diagnostic purposes. However, APSA can be present in a number of exposed but asymptomatic individuals as well as in patients with other interstitial lung diseases who live in areas where keeping pigeons is a common domestic habit. In this study, saliva was evaluated as an alternative means to serum for APSA detection by ELISA using pooled pigeon sera as antigen. Serum and saliva samples obtained from 17 patients with PBD, 14 with idiopathic pulmonary fibrosis (IPF), 19 asymptomatic relatives (AR) exposed to pigeon antigens, and 27 clinical healthy voluntary subjects (CHVS) were tested for IgG and IgA APSA. Our results showed that both fluids obtained from PBD patients exhibited a significantly higher specific IgG antibody activity compared to the other groups. Serum optical density (O.D.) values for PBD were 1.187 +/- 0.738 vs. 0.024 +/- 0.033, 0.255 +/- 0.471, and 0.204 +/- 0.346 for CHVS, AR and IPF, respectively (P < 0.05). Salivary O.D. for PBD were 0.801 +/- 0.447 vs 0.010 +/- 0.011, 0.104 +/- 0.151, and 0.22 +/- 0.447 (P < 0.05). In contrast, serum specific IgA did not discriminate between PBD and IPF patients. In addition, although the PBD group exhibited the highest values of IgA salivary APSA, high levels were also observed in saliva specimens from CHVS, a group of normal individuals who deny pigeon exposure. These findings suggest that measurement of IgG salivary APSA can play a role in the evaluation process of patients with pigeon breeder's disease.

A follow-up study of pulmonary function tests, bronchoalveolar lavage cells, and humoral and cellular immunity in bird fancier's lung

BACKGROUND AND OBJECTIVE

The long-term outcome of bird fancier's lung appears to be variable. The objective of this study is to clarify the sequelae of disease process in bird fancier's lung, with special reference to the humoral and cellular immune responses after avoidance of direct antigen exposure.

METHODS

Five patients with bird fancier's lung were studied for various parameters including pulmonary function tests, cellular profiles of bronchoalveolar lavage (BAL) fluids, determinations of antibodies in BAL fluids and sera, and antigen-induced proliferation of peripheral and bronchoalveolar lymphocytes during the 5 years of follow-up.

RESULTS

Four of five patients showed improvement in pulmonary function, and one showed marked deterioration. This patient's room was close to the pigeon coop where her son was breeding pigeons, resulting in low-grade antigenic stimulation. Three patients demonstrated an increase in CD8+ cells in BAL fluid, but the remaining two showed an increase in CD4+ cells. The levels of IgA antibodies remained unchanged, whereas IgG levels started declining after the first 3 years of follow-up. Antigen-induced proliferation of BAL lymphocytes from all five patients and blood lymphocytes from four of five patients became weaker and gradually approached normal levels. One patient had pulmonary fibrosis and showed significant reduction in pulmonary functions but elevated reactivity of BAL lymphocytes to pigeon antigens.

CONCLUSION

This follow-up study demonstrates persistence of sensitized lymphocytes and antibody production in the respiratory tract and warrants careful evaluation of patients with bird fancier's lung, even after antigen avoidance.

Immune responsiveness to inhaled antigens: local antibody production in the respiratory tract in health and lung diseases

The pulmonary defence mechanism in summer type hypersensitivity pneumonitis induced by Trichosporon cutaneum was investigated. We have studied the antibody response to fungal antigens in sera and bronchoalveolar lavage (BAL) fluids from patients with summer type hypersensitivity pneumonitis, bird fancier's lung, interstitial pneumonia associated with collagen vascular disease (INT-PNE), and from normal volunteers. Antigens extracted from fungi frequently isolated from home environments were used in ELISA to detect IgG and IgA antibodies in sera and BAL fluids. The results of the present study show that antibody titre in the respiratory tract to a variety of fungi from home environments is modulated by ongoing pulmonary inflammation, and that antibody production against inhaled antigens is altered by pulmonary inflammation resulting from diverse pathogenesis. This study concludes that the preexisting pulmonary inflammatory disease alters antibody production in the respiratory tract in response to inhaled fungi, and that the type of alteration depends in part on the etiology of the preexisting disease.

Hypersensitivity pneumonitis associated with home ultrasonic humidifiers

We describe five patients with hypersensitivity pneumonitis (HP) that was related to using home ultrasonic humidifiers. All patients had micronodular infiltrates on their chest radiograph, and their lung biopsy specimens revealed alveolitis with or without epithelioid cell granulomas. Challenge tests were performed on two patients with the humidifier water and three patients using the humidifier. All patients tested exhibited a positive response. Tests for precipitating antibodies against an extract of the humidifier water gave strongly positive reactions in all patients tested. Precipitins to Cephalosporium acremonium and Candida albicans were also present in all cases, whereas precipitins to thermophilic actinomycetes were not detected. Although cultures of the water grew a variety of fungal and bacterial organisms, thermophilic actinomycetes could not be detected. These findings suggest that thermophilic organisms may not be the causative antigens of HP associated with ultrasonic humidifiers. All five patients had an increase in the bronchoalveolar lavage (BAL) lymphocytes that were predominantly CD4+ lymphocytes. The T helper cell count (CD4) to suppressor T cell count (CD8) ratio was significantly higher than that observed in summer-type HP, and lower than that observed in bird fancier's lung, indicating that the phenotypes of the BAL lymphocytes may vary with the type of HP.

Allergens causing bird fancier's asthma

The study investigates to what extent bird feathers contain relevant allergens/antigens involved in bird fancier's asthma. The study group consisted of two budgerigar fanciers, two parrot fanciers and one canary fancier. All subjects complained of asthmatic symptoms, caused by contact with their birds, and they showed a significant bronchial hyperreactivity to acetylcholine. Positive IgE antibody reactions to bird sera as well as to extracts of feathers were observed in RAST. Well-defined major allergenic bands could be detected and identified in the IgE immunoblots with feather extracts as well as with serum proteins of budgerigar, parrot, pigeon, canary, and hen (mol. mass 20-30 kDa and 67 kDa). The most pronounced bands appeared with the extracts of species to which an exposure had taken place. Weaker IgG-binding patterns were also observed. Our results show that inhalable feather dust contains several allergenic components which cross-react with serum allergens/antigens of the same as well as of other bird species. This emphasizes the significance of bird feathers for immediate-type allergic reactions.

[The mechanisms of allergic damage to the bronchoalveolar apparatus in poultry plant workers]

Specific and non-specific mechanisms of defense and damage were studied in 296 poultry breeders, 20 of them were diagnosed the exogenic allergic alveolitis (EAA), the so-called "breeder's lung". The following characters were found: an increase in the blood leucocyte phagocytic activity, non-specific neutrophilic damage values, specific neutrophilic damage and specific lymphocyte damage values, lactate dehydrogenase activity, circulated immune complexes level, immunoglobulins A and M in blood serum in breeders with EAA. Only breeders with service of 1-5 and 11-15 years have shown no changes in non-specific neutrophilic damage values. A decrease in the T-lymphocyte content, theophylline-sensitive and theophylline-stable lymphocyte subpopulations in blood serum of breeders with EAA were observed as well.

Pigeon breeders' lung; IgG subclasses to pigeon intestinal mucin and IgA antigens

Sera from all symptomatics with pigeon breeders' lung and many non-symptomatic pigeon breeders react specifically with the pigeon antigens and in particular pigeon intestinal secretions and isolated pigeon intestinal mucin and IgA. In sera from all 82 precipitin-positive pigeon breeders investigated, IgG1 reacted with both IgA and mucin, while IgG2 reacted predominantly with mucin only. Sera from all 32 symptomatic patients with pigeon breeders' lung demonstrated an IgG3 reaction with mucin, but only three sera showed reactivity against IgA and this was very weak. In contrast, only three out of 27 pigeon breeders with pulmonary pathology other than pigeon breeders' lung and only three out of 23 sera from healthy pigeon breeders showed detectable IgG3 reactivity with mucin. IgG4 from eight sera only reacted with mucin (n = 7) or IgA (n = 1) and showed no consistent pattern between subject groups. Precipitin-negative sera from 30 volunteers with no previous pigeon exposure showed no IgG subclass reactivity with either the pigeon intestinal secretions or the isolated mucin and IgA antigens. These results show specific IgG2 and IgG3 subclass reactivity to pigeon intestinal mucin antigen in precipitin-positive sera from pigeon breeders. Further IgG3 subclass reactivity specific to pigeon mucin is strongly associated with sera from patients with the active pigeon breeders' lung disease.

Relationships between characteristics of exposure to pigeon antigens. Clinical manifestations and humoral immune response

An extensive clinical study has been performed on pigeon breeders in the Canary Islands. Three hundred forty-three subjects have participated in this study through the filling of a clinical and epidemiologic questionnaire. A venous blood sample was also taken from each fancier for a further serologic analysis. Detection of specific IgG antibodies was made by an indirect enzyme-linked immunosorbent assay (ELISA) using pigeon serum as antigenic material. Twenty-nine (8 percent) breeders fulfilled the "classic" pigeon breeders' disease (PBD) criteria. One hundred six (31 percent) had rhinitis, 62 (19 percent) had immediate bronchial symptoms, and 51 (15 percent) suffered from chronic bronchitis. A significant level of specific IgG was detected in 139 (40 percent) cases. Rates were correlated with pneumonitis symptomatology (p < 0.001) and with chronic bronchitis (p < 0.05). There was a significant association between the number of pigeons and the level of sensitization (p < 0.001). Finally, a statistical relationship between the intensity of exposure and specific IgG response was also found (p < 0.001). Titers of specific IgE could not be related either to the reported symptomatology in the questionnaire or to any of the exposure parameters analyzed.

Impairment of lung mucociliary clearance in pigeon fanciers

Lung mucociliary clearance was measured in 15 pigeon fanciers. The study group was subdivided into two: a precipitin-positive group (n = 10; mean +/- SEM age 45 +/- 5 years) with circulating blood precipitins and a precipitin-negative group (n = 5; mean +/- SEM age 40 +/- 3 years) without. Clearance was measured using an objective, noninvasive radioaerosol technique. The data for both groups were compared with those of matched control groups of healthy subjects. The mean +/- SEM area under the tracheobronchial retention curves (AUC) over the 6-h observation period was 257 +/- 27 %h for the precipitin-positive group compared with 177 +/- 16 %h for its control group (p = 0.02)--a high AUC value denoting slow clearance. That for the precipitin-negative group was 282 +/- 34 %h compared with 150 +/- 15 %h for its control group (p = 0.02). Our study illustrates in pigeon fanciers involvement of the conducting airways in that a major defense mechanism of the airways--namely, mucociliary clearance--is substantially compromised. The presence or absence of precipitins appears not to be related to the degree of mucociliary clearance impairment.

Rheumatoid factor activity in serum and bronchoalveolar lavage fluid from patients with acute hypersensitivity pneumonitis

The presence of rheumatoid factor was detected in both serum and bronchoalveolar lavage fluid (BALF) from patients with acute pigeon breeder's disease. IgM rheumatoid factor was positive in 14 of 20 serum samples and 6 of 20 BALF samples by ELISA. In contrast, negative results were found in 20 healthy subjects with a history of avian antigen exposure, as well as in the serum and BALF from 10 normal subjects. The simultaneous presence of rheumatoid factor in serum and BALF occurred in five patients, and four of them revealed high levels of rheumatoid factor in BALF in comparison with serum determinations. These abnormalities may play an important role during the acute inflammatory reaction in hypersensitivity pneumonitis.

A comparison of the seroepidemiology of chlamydial infection in pigeon fanciers and farmers in the U.K

A detailed comparative seroepidemiological study of antibody responses was performed in 271 pigeon fanciers and 100 farmers. Overall 73% of pigeon fanciers had IgG antibodies at a titre greater than or equal to 16 to Chlamydia pneumoniae, 39% to Chlamydia psittaci, and 6.6% to Chlamydia trachomatis. The prevalence of chlamydial antibodies was significantly lower in the farmers at 47% for C. pneumoniae, 6% for C. psittaci, and 2% for C. trachomatis. Both populations were exposed to complex microbiological and antigenic environments: 50.5% of the pigeon fanciers had antibodies to pigeon antigens, 34% to egg membrane, and 0.73% to yolk sac antigen, and 59% of the farmers had antibodies to Micropolyspora faeni, but the high prevalence of chlamydial antibodies could not be attributed to interaction with these antigens. There was considerable overlap of chlamydial antibody responses in the pigeon fanciers but not in the farmers: 36% of the pigeon fanciers had antibodies to C. pneumoniae alone, 5% to C. psittaci alone, and 31% to both agents, whereas only 3% of farmers had antibodies to both C. pneumoniae and C. psittaci. The high prevalence of antibodies to C. psittaci in the pigeon fanciers is compatible with the known avian reservoir for this infection. The particularly high prevalence of antibodies to C. pneumoniae suggests that complex interactions may be occurring in a population exposed to two chlamydial organisms, whereby infection with one species may provoke an anamnestic response against other chlamydial organisms with which the subject has previously been infected.

Experimental models of hypersensitivity pneumonitis

Experimental models of hypersensitivity pneumonitis are important tools for the study of the pathogenesis of this disease. In this paper we review the characteristics of the main animal models developed until now. The HP models in rats seem to be particularly appropriate for studying pigeon fancier's disease and the HP induced by chemicals, as well as for studying mediators of acute lesions induced by immunocomplexes. However, the HP models developed in rats are of less value in the evaluation of other aspects of the pathogenesis of this clinical entity in humans. The murine models of HP offer several advantages: the ease and simplicity of intranasal administration, the ability to produce acute and subacute pulmonary lesions similar to those found in humans, the possibility of reproducing lesions similar to those of nonaffected exposed subjects and the possibility of pharmacologically modulating the process. Their disadvantages lie in the different pulmonary lymphocyte response and the difficulty in reproducing a model of chronic fibrosis. The HP models in rabbits are extraordinarily useful for evaluating the immunological mechanisms through which subjects repeatedly exposed to the antigen do not develop clinical manifestations. However, the rabbit has several immunological differences when compared to humans, and the effect of some immunomodulators in this animal is different. The models of HP in guinea-pigs have as advantages the ease in handling the animals, the possibility of pharmacological manipulation, and the ability to induce an acute phase that is very similar to that observed in humans. The drawback, however, is the low lymphocyte response and the striking eosinophilic reaction that contrast with the bronchoalveolar data found in HP in humans. In conclusion, there is no ideal model to reproduce all the findings observed in humans, suggesting that the experimental animal and the method of developing HP should be selected on the basis of concrete research aims.

A role for IgE in extrinsic allergic alveolitis?

Receptors for the Fc portion of immunoglobulin E (IgE; CD23) can be detected on the surface of alveolar macrophages (AM) in extrinsic allergic alveolitis (EAA), using monoclonal antibodies in immunocytology. More than 50% of AM were positive in 16 of the 20 patients reported here, while the remaining 4 had 11-47% positive cells. Staining with anti-IgE antibody can, in addition, demonstrate endogenous IgE bound to the AM. This suggests that IgE might be involved in the process. Since IgE-mediated asthma is associated with bronchoconstriction, we asked whether EAA patients do in fact exhibit an obstructive component. In 3 out of 10 patients we did indeed find clearly increased airway resistance (greater than 30 kPa x s x l-1). These findings are consistent with the observation of immediate bronchoconstriction observed in some patients upon allergen challenge. Since only 1 of the 20 patients studied was a smoker, and since in the literature the majority of reported cases of EAA are in nonsmokers, we speculate that smoking may interfere with immunological processes leading to EAA.

Immunoglobulin and antibody levels in bronchoalveolar lavage fluid from symptomatic and asymptomatic pigeon breeders

Twenty-one symptomatic subjects with pigeon breeders' lung (PBL) and 10 asymptomatic pigeon breeders, with a similar exposure to pigeon antigens, underwent bronchoalveolar lavage. Total IgG, IgM and IgA in lavage fluid were determined as were specific antibody levels against antigens in pigeon serum and droppings. Results were converted to levels in epithelial lining fluid (ELF) using lavage and serum urea ratios. It was found that symptomatics represent a group that is hyperreactive to pigeon antigens compared with the asymptomatic group with significantly higher IgG, IgM, IgA levels as well as specific antibody levels against pigeon serum and droppings. Paired serum and ELF samples from 12 symptomatic subjects showed significantly elevated IgG, IgM and IgA levels in ELF compared with serum when values were expressed in terms of albumin. This strongly supports the concept of local production of immunoglobulins within the lung after inhaling immunogens as opposed to their diffusion from the vasculature. Results for IgA indicate that any putative protective role for this immunoglobulin is not valid in relation to the prevention of extrinsic allergic alveolitis. Analysis of smoking habits, lung immunoglobulins and response to inhalation challenge confirm the negative influence of smoking on total and functional lung immunoglobulins; however, levels in the ELF of ex-smokers suggest that the effect of smoking is not permanent. Smoking did not prevent responses to inhalation challenge.

Pigeon breeders' lung: pigeon intestinal mucin, an antigen distinct from pigeon IgA

Antigens identified by indirect immunofluorescence staining and specific for sera from patients with pigeon breeders' lung or healthy pigeon breeders, have been isolated from pigeon intestinal mucus. Two antigenic peaks, one pigeon intestinal mucin and the other IgA, were separated by equilibrium centrifugation of water-soluble mucus in a caesium chloride density gradient. Antigenic positive material was identified by a modified double-sandwich ELISA, by inhibition of haemagglutination of turkey erythrocytes and by gel diffusion. Antigenic-positive material co-fractionated on gel-filtration with purified intact and papain digested pigeon mucin, both free of IgA. These studies demonstrate antibodies to two quite different antigens are associated specifically with sera from pigeon breeders, a novel antigen pigeon intestinal mucin and the previously documented pigeon IgA.

Difference in the phenotypes of bronchoalveolar lavage lymphocytes in patients with summer-type hypersensitivity pneumonitis, farmer's lung, ventilation pneumonitis, and bird fancier's lung: report of a nationwide epidemiologic study in Japan

We performed a nationwide epidemiologic study of hypersensitivity pneumonitis (HP) in Japan by questionnaire and found that 835 cases of HP were recognized during the 1980s; 74.4% were summer-type HP, 8.1% farmer's lung, 4.3% ventilation pneumonitis, 4.1% bird fancier's lung, 2.3% other types, such as chemical worker's lung, and 6.8% of unknown causative agent. It was found that the CD4/CD8 ratios of bronchoalveolar lavage (BAL) lymphocytes were significantly different with the type of disease. The ratio was 0.6 +/- 0.1 (mean +/- SEM) in summer-type HP (N = 271), 4.4 +/- 0.7 in farmer's lung (N = 22), 1.6 +/- 0.3 in ventilation pneumonitis (N = 19), and 2.0 +/- 0.5 in bird fancier's lung (N = 19). In farmer's lung, the CD4/CD8 ratio in smokers was 6.2 +/- 1.9 (N = 6) in contrast with 3.4 +/- 0.7 for nonsmokers (N = 16) (p less than 0.05). It has been generally considered that the phenotypes of BAL lymphocytes in patients with HP are predominately CD8 cells. Our present results, however, indicate that the phenotypes of BAL lymphocytes vary with the type of HP, probably depending on factors such as causative agent, smoking, or staging of the disease.

Effect of cigarette smoking on the humoral immune response in pigeon fanciers

Tobacco smoking is associated with increased prevalence of various diseases. In this study, we have used an indirect enzyme-linked immunosorbent assay (ELISA) to investigate the specific IgG response to pigeon serum and its relationship to tobacco smoking. In a large group of pigeon fanciers the development of pigeon breeder's disease and some of the clinical features were also investigated. We found a sensitization rate of 31.9%, a lower degree than that found by other authors, in spite of using a less specific antigen. We also found that fanciers who are current cigarette smokers had significantly lower levels of IgG antibody to pigeon serum (P less than 0.001). Finally, 11.9% of the population had chronic bronchitis as their only manifestation of possible pigeon-related disease. 19.6% of the sensitized fanciers had chronic bronchitis, were non-smokers and had no other risk factor for developing chronic bronchitis.

Measurement of interleukin-6 in bronchoalveolar lavage fluid by radioimmunoassay: differences between patients with interstitial lung disease and control subjects

Bronchoalveolar lavage fluid (BALF) from subjects with a variety of interstitial lung diseases (active sarcoidosis, pigeon breeders' disease (PBD), asymptomatic pigeon breeders, patients with idiopathic pulmonary fibrosis) and from control subjects were assayed for interleukin-6 (IL-6) using a novel radioimmunoassay system. IL-6 was detectable in BALF from all groups, with disease groups showing significantly increased IL-6 levels compared with controls (P less than 0.01 in all cases). When these results were standardized, using urea to compensate for dilution effects in the BALF, only the asymptomatic pigeon breeders had significantly higher IL-6 levels than the controls (P less than 0.025), with all other groups showing no difference. When albumin was used for standardization, both the PBD group (P less than 0.001) and the sarcoidosis patients (P less than 0.01) had considerably lower levels of IL-6 than the control subjects. Using either albumin or urea for standardization, the PBD patients had significantly lower levels of IL-6 than do their asymptomatic counterparts (P less than 0.001 in both cases). This is contrasted by the finding of greatly elevated levels of IgG in the BALF of the PBD patients compared with asymptomatics (P less than 0.001). There was, however, no relation between IL-6 and IgG in any patient group, although the PBD patients had the lowest IL-6 and highest IgG as a group. These findings may suggest a mechanism by which asymptomatic subjects remain free from clinical complaints.

Immunoregulatory abnormalities in patients with pigeon breeder's disease

T-cell suppression induced by concanavalin-A (Con-A) and the prostaglandin suppressor system (PSS) were studied in 14 patients with pigeon breeder's disease (PBD), 12 and 10 asymptomatic breeders, and 8 controls. Our results showed that PBD patients display a significant decrease in T-cell-induced suppression (29.6 +/- 15.3% vs. 61.2 +/- 9.3% in controls p less than 0.05); whereas asymptomatic breeders respond heterogeneously: 5 showed decreased suppression and 7 were within the normal range obtained in controls. In contrast, the patients presented a higher PSS index compared with the other 2 groups, suggesting an inverse relationship between the 2 systems. These findings indicate that there are relevant differences between PBD patients, asymptomatic breeders, and normal subjects in some immune interactions, which may at least partially explain the characteristic cellular and humoral hyperreactivity observed in patients with this disease.

Clearance of 99mTc-DTPA in pigeon fancier's hypersensitivity pneumonitis

The rate of clearance of inhaled 99mTc-DTPA was measured in 20 nonsmoking pigeon fanciers and 7 control subjects. The degree of their avian contact and pigeon-related symptoms were noted, humoral immune response in the form of IgG antibody to pigeon gamma globulin was quantified, and diffusing capacity and total lung capacity were measured. Thirteen fanciers who had a high level of antibody had increased rates of clearance of 99mTc-DTPA (mean half-time clearance of 16.8 [+/- SEM 2.02] min [p = 0.001]) even if they were asymptomatic and even if their diffusing capacity and total lung capacity were normal. Seven control subjects without exposure to pigeon-derived antigens had normal clearance (mean 72.6 [+/- 5.98] min), and seven fanciers with antigen exposure but without an antibody response had intermediate rates of clearance (mean 42.57 [+/- 5.11] min). Clearance was not directly related to the indices of intensity and duration of antigen exposure. The measurement of rate of clearance of 99mTc-DTPA in pigeon fanciers can identify an alteration in pulmonary integrity more subtle than found with conventional pulmonary function tests and may therefore be a useful test for studying the pulmonary response to inhaled antigen and for detecting the earliest stages in the evolution of hypersensitivity pneumonitis.