Extrinsic allergic alveolitis (EAA) is an interstitial lung disease which develops in susceptible individuals after repeated exposure to inhalation antigens. Many antigens are capable of provoking EAA. The best studied forms of EAA include farmer's lung, summer-type pneumonitis and pigeon breeder's disease. Recent reports suggest that the household environment is a potent source of antigens.1 EAA following exposure to feather duvets, steam iron, or cat fur has been documented.2–4 The spectrum of antigens varies not only with environment but also with different geographical locations.5 The immune response to inhalation antigens can be detected by production of serum specific immunoglobulin G (IgG).6 The diagnostic value of specific serum IgG in EAA patients is controversial. No physiological ranges for specific IgG against possible causative antigens have been established for the Czech population. The aim of our study is to discover whether there are any differences in specific IgG in sera of potentially repeatedly exposed and nonexposed individuals and above all to detect possible differences in concentrations of specific serum IgG among subjects with subacute EAA, chronic EAA and subjects without EAA.

The numbers of patients in groups according to their history of exposure are included in Table 5. Possible occupational exposure was detected in 10 patients (exposure to bird antigens in 2 cases, mammals 5 cases, moulds 3 cases). Sixteen patients reported farming activities in their free time, 8 were exposed to bird antigens, 5 to mammals and 4 to moulds. Forty-four patients indicated household exposure – 11 kept birds, 12 mammals, 15 were exposed to moulds and 6 to dust and possibly mites.

Possible occupational exposure was detected in 7 EAA patients (bird antigens in one case, mammals in four cases and moulds 4 times). Two patients with EAA were involved in farming activities with exposure to bird antigens. Nine EAA patients kept birds, 11 kept a mammal at home, six claimed exposure to moulds at home and five reported a dusty environment. Seven EAA patients had more than one possible source of antigen inhalation.

Serum concentrations of total IgG were within normal limits (8–13.5g/l) in all examined individuals. Serum concentration of Aspergillus fumigatus, Candida albicans, moulds 1 and 2 IgG was significantly higher in subjects with confirmed exposure to relevant inhalation antigens (p<0.05). Patients exposed to parrots (Ge92) and hair 1, 2 (ex1, ex2) had a significantly higher serum concentration of specific IgG than patients with no documented exposure (p<0.05). Subjects who had taken precautions to reduce their exposure to mites (bedding made of hollow fibres, no carpets, no curtains, etc.) had lower serum IgG to Dermatophagoides pteronyssinus, Dermatophagoides farinae, Dermatophagoides microceras and Glycophagus domesticus than the rest of examined individuals (p<0.05). Concentrations of specific IgG in serum of exposed and nonexposed individuals are summarized in Table 6.

Concentrations of specific IgG in serum of control group, patients with subacute EAA and chronic EAA are summarized in Table 7.

While assessing antibody response to inhalation antigens in EAA patients, it is important to choose relevant antigens. This study is the first one to test a broad spectrum of response to antigens; a spectrum of selected antigens and differences in specific serum IgG concentrations between exposed, nonexposed and EAA populations are further discussed. Most of the subjects in the group reported exposure to inhalation antigens in their household environment. We can assume that exposure to inhalation antigens in a household environment is continuous, which makes the presence of specific IgG against the offending antigen more likely.7,8 Antigens of moulds are ubiquitous – particularly the investigated species (Aspergillus sp., Cladosporium sp., Alternaria sp. and Penicillium sp.) which are commonly detected in damp buildings in central Europe.9,10Candida sp. is not usually detected in samples of house dust, but it can be found in oral or gut fungal microbiofilm in healthy individuals and its role in developing EAA in farm workers has been documented.11–13 EAA induced by endogenous C. albicans was observed as well.14

We found a significantly higher serum concentration of specific IgG to mixtures of antigens moulds 1 and 2 in exposed individuals (Table 4). A significant difference was observed also in A. fumigatus and C. albicans IgG concentrations between exposed and nonexposed subjects. No difference in serum concentrations of moulds antibodies in EAA patients and subjects without EAA was found. We conclude that in individuals with household exposure to moulds, concentrations of specific serum IgG will not help us to confirm diagnosis of EAA.

Some of our patients also had a history of occupational exposure to moulds. They were also tested for Micropolyspora sp. and Thermoactinomyces sp. serum specific IgG, because both of these have been detected as leading to antigens of farmer's lung in Finland, India, China, Spain.15 Antigens causing EAA in Czech farmers have not been identified, although the relevance of tested antigens has been highlighted by various authors.16 Since no differences in serum anti-Micropolyspora sp. and anti-Thermoactinomyces sp. IgG concentration between exposed and nonexposed subjects were found, we suggest these moulds may not trigger farmer's lung disease in Czech farmers. Similarly, neither Micropolyspora sp. nor Thermoactinomyces sp. were found in Switzerland, Canada or United States,17 perhaps due to different geographical conditions.

Mites as well as moulds are ubiquitous organisms and exposure history data are difficult to obtain. Exposure occurs not only at home (a dusty household environment was taken into account) but also in the farming population and among bird keepers.18,19 Although no case of EAA provoked by exposure to mites has been described, EAA developed after exposure to insect proteins is well known (miller's lung, lycoperdonosis). Six patients in our study group had a history of exposure to dust in the home. The panel of investigated antigens (Table 4) included D. pteronyssinus, D. farinae, D. microcerans and Euroglyphus maynei, which are known to be house dust mites. Concentration of specific IgG for D. pteronyssinus, D. farinae and D. microceras was found to be higher in serum of exposed subjects than in nonexposed individuals. Furniture mites G. domesticus feed on moulds and the association between G. domesticus and the occurrence of moulds is likely. Patients exposed to house dust had higher serum concentration of specific IgG against this mite than those not exposed. The observation was not supported by different serum IgG concentrations in EAA vs. control group. The farming population might be exposed to so-called storage mites: Acarus siro, Lepidoglyphus destructor and Tyrophagus putrescentiae. A. siro occurs as an agricultural pest, T. putrescentiae is a pest in many foods including dog food. L. destructor can be found in animal food, it consumes moulds, mostly Alternaria sp. and Penicillium sp. We found a significantly higher serum IgG concentration against A. siro and T. putrescentiae in patients with subacute EAA and a corresponding exposure history than in the patients with chronic EAA and the control group. We suggest that mites’ antigens should be considered as possible provoking agents in subjects with a history of exposure to dust and moulds who have suspected EAA. Particles of mites smaller than 5μm can penetrate the distal respiratory tract and may be able to start an immune response leading to EAA. Moreover, since mites antigens provide strong proteinase activity, they might modify the immune response to other inhaled antigens.20 Brown et al. showed that major antigen of D. pteronyssinus – Der p1 – can modulate the adaptive immune system by cleavage of CD23 and CD25, which may promote an allergic inflammatory response.21 Further, Der p1 disrupts epithelial tight junctions, which facilitates the transport of allergen across the epithelium. Der p1 and other mite antigens cause release of proinflammatory cytokines from bronchial epithelial cells, mast cells and basophils.22 They cause degradation of surfactant proteins SP-A and SP-D.23 Surfactant properties of SP-A and SP-B were found to be changed in EAA patients.24 Higher serum levels of SP-D in EAA patients with severe lung function impairment and better recovery over time documented by Jansen et al. may be the consequence of more rapid surfactant turnover.25

Furrier's lung and animal handler's lung are caused by animal fur dust, proteins, urine, serum and pelts of rats and gerbils.26 Even though exposure to animal fur, serum and secretions could be expected in farmers and pet keepers, we found no report in the literature about the measurement of the specific serum IgG concerned. We found a significantly increased serum IgG against a mixture of antigens hair 1 and hair 2 in exposed individuals compared to subjects without a history of exposure to these antigens. We found no differences between serum concentrations of antibodies against animal antigens in EAA patient and the control group, which may discourage use of these specific IgG in to confirm diagnosis.

Bird fancier's lung is one of the best studied and most frequent forms of EAA. Several studies have aimed to quantify serum antibodies in this form of EAA. The incidence of serum specific IgG in asymptomatic bird keepers is 40%.7,8 McSharry et al. proposed that the presence of serum antibodies may reflect sub-clinical inflammation, but no studies involving longitudinal monitoring of specific IgG concentration in serum of exposed individuals are available.27 Patients, who were exposed to avian inhalation antigens in their childhood or during later life, may develop feather duvet lung after exposure to bedding filled with goose feathers.28 We documented higher concentration of specific IgG against mixture of parrot derived antigens in exposed individuals than in the nonexposed group. Generally, except for mixture of antigens Feather 1, significantly higher serum IgG concentrations of all groups of bird antigens were observed in subacute EAA patients compared to the control group. Patients with chronic EAA tested for Feather 3 and budgerigar had higher appropriate specific IgG serum concentrations than the control group.29,30

It is unlikely that patients with EAA are exposed to just a single inhalation antigen. Farming population can be exposed to moulds, mites, avian proteins and animal's fur, serum and urine. Thus it may be difficult to differentiate trigger antigens.

ImmunoCAP technology was used to measure specific serum IgG concentrations. Previous studies have proved that results achieved by ImmunoCAP method are consistent with precipitation technique.31 It could be argued that the control group did not consist of healthy volunteers, and patients with various interstitial lung diseases were involved. Yoshizawa et al. suggested that preexisting inflammatory disease alters the antibody response to inhaled antigens and that modulation of antibody response is dependent on the preexisting condition. We find that the enrolment of patients with interstitial lung diseases other than EAA as a control group is useful not only as a control group per se but also from the differential diagnostic point of view.32

We conclude that concentrations of serum IgG against moulds and mammals antigens does not differentiate between exposure and EAA disease. On the other hand, higher serum concentrations of specific IgG against mites and avian antigens are found in exposed individuals as well as in subacute and chronic EAA patients. These two antigen groups and the antibody response to them should be further studied, because they can help us to clarify the pathogenesis of EAA and can serve as useful diagnostic tools. Finding higher specific IgG concentrations should lead to a detailed examination of the patient's history with particular reference to inhalation exposure. Detection and elimination of the source of inhalation antigen is also one of the steps in the treatment of EAA patients. Only relevant specific IgG should be tested, as documented by our research into mould specific IgG concentrations in the Czech farming population.

The authors have no conflicts of interest to declare.