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Indoor allergens: Identification and quantification
Environment International, Vol. 12, pp. 115-120, 1986 Printed in the USA. All rights reserved.
0160-4120/86$3.00 + .00 Copyright©1986Pergamon Journals Ltd.
INDOOR ALLERGENS: IDENTIRCATION AND QUANTIFICATION Charles E. Reed and Mark C. Swanson Mayo Clinic, Rochester, Minnesota55905 USA (Received 26 February 1985; Accepted 4 November 1985) A large number of allergens occur in the air of the home and many work sites. Almost any organic dust or volatile chemical reactive with proteins can cause allergic respiratorydisease: allergic rhinitis, asthma, and hypersensitivitypneumonitis (extrinsic allergic alveolitis). If the exposure continues several years after the disease begins there may be permanent disability, so recognition and control of exposure are important. Techniques now exist to sample the particulate antigens suspended in the air and assay them by sensitive immunochemicalmethods.
The Allergens
Introduction The various allergens each arise from particular conditions, so the type and amount o f allergen in the air depends on the circumstances at the site. M a n y allergens are products o f growing organisms; each o f these organisms has its own habitat and conditions that favor its growth. Even in dwellings allergens vary with the construction, furnishings, climate, and season, and with various unique conditions within the building. At the work site the list o f occupational allergens is almost as long as the list o f occupations, for virtually any vapor or aerosolized mist that contains proteins or low molecular weight molecules that can react covalently with proteins can sensitize some o f the workers that are exposed. Most o f the allergens that have been characterized chemically are highly soluble glycoproteins with molecular weights o f 10,000 to 100,000 daltons. In general, for sensitization to occur the antigen must be present in the air in relatively high concentrations and for a rather prolonged period o f time. Once sensitization has occurred, however, a brief minute exposure m a y suffice to elicit an allergic reaction. Particle size is another important factor in allergic reactions. Large particles 10 to 50 ~ m mean mass aerodynamic diameter impact in the nose; optimum size for intrathoracic airway deposition is 1 to 10 ~m; and for deposition in the terminal airways is less than
Household O f the allergens that arise within the home, pyroglyphid mites o f the genus Dermatophagoides are the most widespread (Spieksma et al., 1969; Sinha and van Bronswijk, 1971). These mites, whose food source is human and other animal epidermal scales, have a worldwide distribution, but because they require high humidity they thrive in some climates and are less important in others. At one time it was thought that D. pteronyssinus was the most important house dust mite in Europe and D. farinae in North America, but it is now known that the humidity in the particular house is the determining feature. D. farinae tolerates slightly lower humidity. Allergic disease from house dust mites is most frequent in marine West Coast, Mediterranean, and tropical climates where mild humid winters provide the optimum conditions for these mites to grow. Mattresses and bedding, because o f moisture from the sleeper, and carpets because the floor is cooler and humidity higher, are their main habitats. Mites are more c o m m o n on the ground floor than upper stories and are rare in hotels. The homes o f patients who have asthma associated with house dust allergy are more humid and have more mites than control homes in the same community (Korsgaard, 1983).
1 p.m.
115
116 Studies in Ohio, which has a continental climate with warm humid summers and cold dry winters, show that the numbers of live mites is at a maximum during the summer when windows are open and ventilation is good. In the winter the humidity indoors drops and the mites die (Arlian et al., 1982). It seems that house dust allergy in colder climates is most important in the fall, but in milder climates symptoms change little with the seasons. Mites are too small to be seen with the naked eye, but far too large to become airborne. The major source of respirable dust particles seems to be fecal pellets which are of a size to be efficiently filtered in the nose (Tovey et al., 1981). Our own more recent studies indicate that more than one-half of mite antigen is in particles less than 5/~m, a size that can readily reach the lungs (Swanson et al., 1985). Pets often cause respiratory allergy. Cats, being the most frequent offender, have received the most study. The main antigen, called Cat-1, is an important component of saliva, though small amounts can be found in other body fluids (Bloch et al., 1974). The antigen becomes airborne in 1 to 10 p.m particles presumably after it dries and flakes off the fur (Swanson et al., 1985). The antigen from dogs has not been characterized as thoroughly as cats, although it appears to be similar (Hoffman, 1980). Other pets, such as mice, guinea pigs, gerbils and hamsters also shed allergens and we have found mouse urinary protein in some dwellings in higher concentrations than in research laboratories where it causes occupational respiratory allergy. Feathers have long been considered to be an important antigen in the home, but it now appears that the symptoms and positive skin tests arise more often from mites growing in pillows and bedding rather than bird proteins. Hypersensitivity pneumonitis associated with the hobby of keeping pigeons is the most common illness from exposure to bird antigens. Occasionally, other birds are responsible. Parakeets (budgerigars) can cause an especially serious problem because the disease onset is slow and insidious and may have progressed to pulmonary fibrosis before diagnosis. Pigeon antigens get into the air from the droppings, but their original source is serum proteins secreted into the gut (Barboriak et al., 1969). Insect antigens are highly allergenic, and cockroaches are an important cause of asthma, especially in inner city homes of the lower socioeconomic class (Homberger et al., 1979; Colten et al., 1977). Occupational asthma from insects is common in entomology laboratories. Many authors mention molds as an important indoor allergen, most of the molds cultured indoors have entered from outdoors. In unusual conditions where moisture and nutrients provide the necessary habitat, a mold can flourish sufficiently to cause allergic dis-
C.E. Reedand M. C. Swanson ease (Mathews and Soloman, 1983; Solomon, 1975). In such cases the mold is obvious, but house plants are not a quantitatively significant source of allergenic molds (Berge et al., 1982). On the other hand, microorganisms growing in home humidifiers, air conditioners, and heating systems occasionally do cause asthma or hypersensitivity pneumonitis (Burke et ai., 1977; Banaszak et al., 1970; Fink et al., 1971a, 1971b). This source of indoor allergens is more important in factories and large office buildings (Reed et al., 1983).
Occupational
In his recent review of occupational asthma, Parkes (1982) includes an up-to-date listing of the antigens. Only the more common ones are mentioned in Table 1, a complete listing is beyond the scope of this article. Additional antigens are being recognized not only in new industrial processes, but in old established occupations as well. For example, several groups of investigators have found that glycophageous storage mites are the chief source of antigens responsible for asthma after exposure to hay or grain dust (Cherniack et al., 1974; Agha and Gnanasakthy, 1981; Engstrom et al., 1982). Urinary proteins are the major antigen responsible for asthma and rhinitis from working with laboratory mice, rats and guinea pigs (Longbottom et al., 1977, Swanson et al., 1983). Of the many wood dusts that cause asthma, the most thoroughly studied is western red cedar, Thuja plicata (Chan-Yeung, 1982). Plicatic acid, a low molecular weight substance isolated from the wood, reproduces the airway obstruction, but the mechanism of the obstruction may or may not involve IgE or any other immunological reaction. Although most small highly reactive molecules act as haptens and evoke an IgE reaction, the diisocyanates have not yet been proved to act in this way, and may cause asthma through some other mechanism, possibly by reacting with cell surface receptors (Bernstein, 1982; Butcher et al., 1977). The complexity of the immunological events that occur after inhalation of highly reactive molecules has been illuminated by studies of workers exposed to trimellitic anhydride (Patterson et al., 1982). Not all agents suspected of being airborne allergens turn out to be so. Our studies of asthmatic patients exposed to formaldehyde gas failed to confirm that it caused airway obstruction (Frigas et al., 1984). Sometimes the antigen causing an occupational allergy is not the obvious one. For example, workers in the coffee industry may have asthma not only to green coffee bean dust but also from castor bean dust remaining in the burlap sacks that had previously been used to ship castor beans (Butcher et al., 1978; Johansson et al., 1982).
Indoor allergens
117 Table 1. Indoor allergens.
1. Household dwellings A. House dust mite B. Pets C. Cockroach D. Molds
2. Agricultural and food processing A. Grain dust (? storage mites) B. Moldy hay, silage or bedding C. Bagasse D. Soy, castor, coffee beans E. Sunflower seed, cottonseed, flaxseed F. Wheat flour, rye flour, buckwheat G. Papain H. Shellfish, fish I. Mold on cheese (Penicillium) 3. Woodworking A. Western red cedar B. California redwood C. Maple bark (Cryptostroma corticale) D. Moldy sawdust (both molds and Thermophilic actinomycetes) E. Tropical hardwoods 4. Chemical industry A. Plastics (e.g., diisocyanates, trimellitic anhydride) B. Metals (e.g., nickel, platinum)
C. Pharmaceuticals D. Detergents (Bacillus subtilis enzymes) 5. Textileindustry A. Byssinosis(cotton bract dust) B. Cold water spray air conditioners 6. Cosmetics A. Hair dyes B. Bleaches 7. Laboratory animals A. Rodent urine B. Insects 8. Bird raising A. Pigeons B. Parakeets (Budgerigars)
9. Air conditioners A. Thermophilic actinomycetes
B. Chilled water mist (humidifier fever)
Measurement of Antigens in Indoor Air Quantification o f indoor air pollutants is necessary to assess their importance and to follow the efficacy o f actions taken to control their exposure. Traditional methods o f quantifying allergens in the air depended on counting morphologically identifiable particles like pollen grains or culturing viable organisms like molds. Only recently have methods become available for measuring the amorphous nonviable antigens that are important indoors. Well-standardized techniques have
long existed to measure total particulate solids and many volatile chemicals. These same principles and sampling equipment can be adapted to the measurement o f levels o f antigens in the indoor air and to determine their particle size. T o date application o f these principles has been limited. Clark et aL (1976) found a correlation between the numers o f particles 2 #m and less in diameter in the air after housecleaning and the reduction in peak flow rates o f the children with house dust induced asthma. Chapman et al. 0 9 8 3 ) were unable to detect house dust mite antigen in the air o f undisturbed rooms, but did find antigen during domestic activity. Using a cascade impactor they found that 80% o f the airborne antigen was associated with particles greater than l 0 ~ m in diameter. Some o f these particles had the appearance o f mite feces. Using the same methods, Carswell et al. (1983) estimated the dose of house dust mite antigen inhaled by a 1-month old infant and concluded that it is not sufficient to sensitize. Our studies o f airborne antigens began in 1977 as part o f an investigation o f an outbreak o f hypersensitivity pneumonitis from a contaminanted chilled water spray wash air conditioning system (Reed et al., 1983). Slime growing in the chilled water reservoirs contained an array o f antigens that reacted with IgG antibodies in the serum o f the affected workers and also elicited a positive inhalation challenge test. By appropriate immunochemical procedures it is possible to measure both the antibody and the antigen. To measure airborne antigen at work sites within the plant, particles larger than 0.3 ~Lm were collected on a 20 x 25 cm fiberglass filter paper sheet using a high-volume air sampler (GMS-3210 Accu-Vol, General Metal Works, Cleves, OH). The antigens were eluted from the filter paper by descending chromatography into a collecting beaker. After dialysis and lyophilization the antigens were assayed by a radioimmunoassay inhibition technique that e m p l o y e d antiserum from affected workers. We found levels o f antigen in the air at the work site o f 0.5 to 15 ~m/m 3. Effective actions reduced the antigen in the water and as a result the level of antigen in the air declined gradually over the next 2 yr to levels o f 0.001 to 0.0001 ~Lm/m3, values equal to or less than levels measurable in the outdoor air of the community. This same technique with modifications can be used to measure any antigen, provided that an antigen reference standard exists and that serum containing either IgG or IgE antibody is at hand. Furthermore, an Andersen cascade impaction attachment is available for the Accu-Vol sampler (Andersen Samplers Inc., Atlanta, GA), so that the amount o f antigen in various particle sizes can be determined. Thus, we now have the technology to investigate many interesting questions. With several samplers operating simultaneously, several sites can be compared to determine
C.E. Reed and M. C. Swanson
118
DISTRIBUTION OF ,~LIRRGEN ACTMTY IN AIRBORNE PARTICLES OF DEFINED SIZES STAGE 1 >4.1 u
X TOTAL ~
STAGE 2 <<..1 u>2.3u
STAGE 3 <2.3u>1.4.u
STAGES 4J¢5 <1.4u
ACTIVITY
60
50
40
30
20
10
~
; / / / V////] / / / / V////J / i / / V//I/J / ,, / I V / / / A ///i
~ I I I
.. - . . . . . i Y / / / / V / Z / / J 1. - . . - . . iF / / " "~ V / / I / ] I'. - - ' . " Y " / / / V I / / / J I ' . - ' . "." ~Y i / i / V / / / / ~ .....i///
CAT /M.LERGEN MITE ALLERGEN SAMPLES BY ACCU-VOL wl'n-I ANDERSEN CASCADE IMPACTION HEAD
Fig. I.
differences in concentration at different places. The same site can be sampled sequentially to determine different concentrations at different times or to test the effect of interventions undertaken to alter the concentration. We have measured mouse urinary proteins and mouse pelt proteins in the air of an animal quarters, in an immunology laboratory where there were five mice, and in the same laboratory over the weekend (Agarwal e t a l . , 1982). Airborne antigen content varied from 1.8 to 825 p.g/m3 depending on the site and degree of work activity in the room. Thin layer electrofocusing of the air sample filter eluate showed bands that were common to those produced by mouse urine, mouse pelt extract and mouse serum albumin. No single one of their sources contained all the bands of the filter eluate. Studies with guinea pig allergens gave similar results, but guinea pig urine proteins were the dominant antigen (Swanson, 1983). Most of the antigen occurred in particles larger than 5 p.m or smaller than 0.8 p.m in diameter. In a Rochester, MN, home with three cats, we found that most of the cat antigen was contained in particles less than 5 p.m (Table 2). Also, in contrast to the studies of Chapman e t a l . (1983) we found airborne house dust mite antigen was also chiefly in particles less than 4 p,m, too small to be associated with mite fecal pellets. The concentration of both cat and mite antigen greatly increased for 20 min after making a bed where the cat often slept. Rather surprisingly,
the particle size of the antigen was not much different. The antigen was predominantly in particles less than 5 p.m. The Accu-Vol sampler is not suitable for home sampiing. It is too noisy. Also, sampling the relatively small finite volume of air in a home requires either intermittent sampling or continuous sampling at flow rates that will have only a negligible cleaning effect on the total volume of air being sampled. We have designed quiet samplers that operate in the range of 1 to 6 L/sec (Swanson e t al., 1984). Substitution of Gortex ® for fiberglass improves the efficacy of elution of the allergen and avoids the necessity for lyophilization which may destroy labile antigens. However, the sensitivity of the assay techniques will not permit sampling volumes much smaller than 50 m 3. Duration of sampling depends on the concentration of the antigen under consideration. Aeroallergen
quantitation
Airborne allergen levels from middle class single family dwellings in Rochester, MN, and crowded apartments in Harlem, NY, provide contrasting information about the prevalence and relation concentrations of various aeroallergens (Table 3). In Rochester, dwelling 1 had three pet cats, dwelling 4 had two, and dwelling 3 had one pet cat. Dwelling 8 had three pet guinea pigs, and dwelling 9 had one. Thus, the amount of animal antigen in the air is proportional to the number of animals in the house.
Indoor allergens
119 Table 2. Duration of suspended antigens associated with particles of various sizes in the air after making a bed. Antigen Concentration
(pg protein/m') Mite
Cat
Particle Size
5 rain
20 min
24 h
20 rain
24 h
Larger than 4.1 ttm <4.1 t~m >2.3 ttm <2.3 t~m > 1.4 ~,m < 1.4 t~m >0.8 tan Smaller than 0.8 t~m
83,920 162,790 176,420 218,490 94,470
17,520 63,280 24,170 44,510 40,430
240 520 220 470 290
14,460 9,110 3,170 7,720 15,090
6,550 6,430 4,460 5,510 14,380
The concentration o f house dust mite antigen in the air was similar in these homes as was the concentration o f cat in homes with cats. However, the concentration o f cockroach and m o u s e urinary protein was m u c h higher in the air o f lower socioeconomic homes. In some o f these tenements the concentration o f mouse urinary protein was similar to concentration in the air o f a laboratory where there were several mice and where researchers allergic had symptoms.
Control of Indoor Allergens Control o f exposure to indoor allergens offers the most effective strategy for treating the respiratory allergic disease they cause. Prompt accurate diagnosis is the cornerstone o f success. Promptness is important because continued exposure in cases o f asthma leads to airway hyperirritability and airway obstruction that can persist months or years after the exposure ceases (Bernstein, 1982). Continued exposure in cases o f hypersensitivity pneumonitis leads to p u l m o n a r y fibrosis and permanent p u l m o n a r y disability (Fink et al., 1982). A c c u r a c y is equally important. Just as a missed
diagnosis can be tragic, an error in the other direction can also be harmful. Mistaken advice to change occupation or home can seriously disrupt a person's life by economic loss or by useless restrictions on his activity and place unnecessary burdens on his family as well. Each antigen has its own particular means o f control. Sometimes identification o f the antigen allows simple direct action such as removing a cat from the house, but usually control is more difficult. Improved ventilation m a y suffice, but in cold climates energy costs for heating a large flow of air may be prohibitively expensive. For microbial antigens, it is often possible to improve ventilation in a damp environment that is responsible for promoting growth, or to add an antimicrobial chemical to contaminated chilled water air conditioning systems. Cleaning is quite helpful when the contamination is obvious. Cleaning not only removes antigen but, clean, uncluttered buildings provide fewer niches where nutrients and humidity allow microbes or arthropods to grow. In occupational exposures engineering changes in plant design and materials handling are effective. For example, toluene
Table 3. Indoor allergen concentrations (picograms of protein per cubic meter). Dwelling Rochester 1
Mite
Cat
2 3 4 5 6 7 8
1610 370 1600 2600 4090 5570 2790 NDa
92,000 < 1,000 17,000 51,000 ND ND ND < 1,000
9
ND
<,1000
2400 3700 3140 2160 3220
5,110 6,290 55,900 13,150 14,680
Harlem 1 2 3
4 5
NDa = not determined.
Roach
Mouse Urine
Guinea Pig Urine
< 1,000
<3
< 1,000
ND ND ND ND ND < 1,000 ND
<3 <3 <3 <3 <3 <3 <3
ND
<3
< 1,000 < 1,000 < 1,000 < 1,000 ND ND 495,000 118,000
2960 430 230 1240 610
ND ND ND ND ND
20,010 16,240 25,100 42,480 43,430
120
diisocyanate spills can be reduced by keeping the chemical contained at all times. Monitoring the concentration o f antigen in the air is useful in order to follow the effectiveness of control measures in those cases where eradication of exposure is not feasible. In some occupational exposures such as farming, control of the antigen at the source is impossible. Instead, personal protective equipment is desirable. Filter masks have not proved to be as satisfactory as laminar flow helmets that provide a curtain of filtered air in front of the face. Occasionally, as a last resort, the only means of controlling the disease is a change of occupation.
References Agha, M. and Gnanasakthy, A. (1981) A cluster of analysis of the effects of storage mites on allergens in relation to certain occupations and living conditions, Clin. Allergy 11,499-504. Agarwal, M. K., Dahlberg, M. E., Twiggs, J. T. and Yunginger, J. W. (1982) Immunochemical measurement of airborne mouse allergens in a laboratory animal facility, J. Allergy Clin. lmmunol. 69, 522-526. Arlian, L. G., Bernstein, I. L. and Gallagher, J. J. (1982) The prevalence of house dust mites, Dermatophagoides spp, and associated environmental conditions in homes in Ohio, J. Allergy Clin. lmmunol. 69, 527-532. Banaszak, E. F., Thiede, W. H. and Fink, J. N. (1970) Hypersensitivity pneumonitis due to contamination of an air conditioner, New Engl. J. Med. 283, 271. Barboriak, J. J., Edwards, J. H. and Fink, J. N. (1969) Excretions of pigeon serum proteins in pigeon droppings, Proc. Soc. Exp. Biol. Med. 132, 907. Bernstein, I. L. (1982) Isocyanate-induced pulmonary diseases: A current perspective, J. Allergy Clin. lmmunol. 70, 24-31. Berge, H. A., Boise, J. R. and Solomon, W. R. (1980) Microbial prevalence in domestic humidifiers, Appl. Environ, Microbiol. 39, 840. Berge, H. A., Solomon, W. R. and Mulenberg, M. S. (1982) Evaluation of indoor plantings as allergen exposure sources, J. Allergy Clin. lmmunol. 76, 101-108. Bloch, K. J., Lowell, F. C. and Ohman, J. L., Jr. (1974) Allergens of mammalian origin. III. Properties of a major feline allergen, J. lmmunol. 113, 1668. Burke, G. W., Carrington, C. B., Fink, J. N., Gaensler, E. A. and Strauss, R. (1977) Allergic alveolitis caused by home humidifiers. Unusual clinical features and electron microscopic findings. J. Am. Med. Soc. 238, 2705-2708. Butcher, B. T., Davies, R. J., O'Neil, C. E. and Salvaggio, J. E. (1977) The in vitro effect of toluene diisocyanate on lymphocyte cyclic adenosine monophosphate production by isoproterenol, prostaglandin, and histamine, J. Allergy Clin. lmmunol. 60, 223. Butcher, B. T., Karr, R. M., Lehrer, S. B., and Salvaggio, J. E. (1978) Coffee worker's asthma. A clinical appraisal using the radioallergosorbent test, J. Allergy Clin. lmmunol. 62, 143-148. Carswell, F., Clark, J., Platts-Mills, T. A. and Robinson, P. (1983) The dose of house dust mite antigen (PI) inhaled by infants aged one month, Ann. Allergy 51,539-542. Chan-Yeung, M. (1982) Immunologic and nonimmunologic mechanisms in asthma due to western red cedar (Thuja plicata), J. Allergy Clin. lmmunol. 70, 32-37. Chapman, M. D., Piatts-Mills, T. A. E. and Tovey, E. R. (1981)
C.E. Reed and M. C. Swanson Mite faeces are a major source of house dust allergens, Nature 289, 592-593. Cherniack, R. M., Tse, K. S. and Warren, P. (1974) Hypersensitivity reactions to grain dust, J. Allergy Clin. lmmunol. 53, 139-149. Clark, R. P., Cordon-Nesbitt, D. C., Malka, S., Preston, T. D. and Sinclair, L. (1976) The size of airborne dust particles precipitating bronchospasm in house dust sensitive children, J. Hygiene (Camb.) 77, 321-325. Colten, H. R., Picone, F. J., So, J., Strunk, R. S. and Twarog, F. J. (1977) Immediate hypersensitivity to cockroach. Isolation and purification of the major antigens, J. Allergy Clin. ImmunoI. 59, 154-160. Engstrom, B., Hillerdal, G,, Johansson, S. G. O., Wiren, A. and Zetterstrom, O. (1982) Mites living in hay: An important allergen source?, Allergy 37, 475-479. Fink, J. N., Resnick, A. J. and Salvaggio, J. E. (1971a) Presence of themophilic retinomycetes in residential heating systems, Appl Microbiol. 22, 730. Fink, J. N., Banaszak, E. F., Thiede, W. H. and Barboriak, J. J. (1971b) Interstitial pneumonitis due to hypersensitivity to an organism contaminating a heating system, Ann. Intern. Med. 74, 80. Frigas, E,, FiUey, W. V., and Reed C. E. (1984) Bronchial challenge with formaldehyde gas: Lack of bronchoconstriction in 13 patients suspected of formaldehyde-induced asthma, Mayo Clin. Proc. 59, 295-299. Hoffman, D. R. (1980) Dog and cat allergens: Urinary proteins or dander proteins?, Ann. Allergy 45, 205-206. Homburger, H., Kang, B., Vellody, D. and Yunginger, J, W. (1979) Cockroach cause of allergic asthma. Its specificity and immunologic profile, J. Allergy Clin. lmmunol. 63, 80-86. Johansson, S. G., Osterman, K. and Zetterstrom, O. (1982) Coffee worker's allergy, Allergy 37, 313-322. Korsgaard, J. (1983) Mite asthma and residency. A case-control study on the impact of exposure to house-dust mites in dwellings, Am. Rev. Respir. Dis. 128, 231-235. Longbottom, J. L., Newman-Taylor, A. and Pepys, J. (1977) Respiratory allergy to urine proteins of rats and mice, Lancet 2, 847-849. Mathews, K. P. and Solomon, W. R. (1983) Aerobiology and inhalant allergens, in Allergy: Principles and Practice, 2nd ed., E. Middleton, C. E. Reed, and E. F. Ellis, eds., pp. 1143-1202. C. V. Mosby Company, St. Louis, MO. Parkes, W. R. (1982) Occupational Lung Disorders, 2nd ed., pp. 416-422. Butterworths, London. Patterson, R., Pruzanski, J. J., and Zeiss, C. R. (1982) Immunology and immunopathology of trimellitic anhydride pulmonary reactions, J. Allergy Clin. lmmunol. 70, 19-23. Reed, C. E., Swanson, M. C., Lopez, M., Ford, A. M., Major, J., Witmer, W. B., and Valdes, T. B. (1983) Measurement of IgG antibody and airborne antigen to control an industrial outbreak of hypersensitivity pneumonitis, J. Occup. Med. 25, 207-210. Sinha, R. N. and van Bronswijk, J. E. (1971) Pyroglyphid mites (Acari) and house dust allergy, J. Allergy Clin. lmmunol. 47, 31-52. Solomon, W. R. (1975) Assessing fungus prevalence in domestic interiors, J. Allergy Clin. lmmunol. 56, 235. Spieksma, F. T. M., Varekamp, H., and Voorhorst, R. (1969) House Dust Atopy and the House Dust Mite. Stafeus, Leiden. Swanson, M. C., Agarwal, M. K., Yunginger, J. W. and Reed, C. E. (1984) Guinea pig derived allergens: Clinicoimmunologic studies, characterization, airborne quantitations and size distribution, Am. Rev. Resp. Dis. 129, 844-849. Swanson, M. C., Agarwal, M. K., and Reed, C. E. (1985) An immunochemical approach to indoor aeroallergen quantitation with a new volumetric air sampler. Studies with mite, roach, cat, mouse, and guinea pig antigens, J. Allergy Clin. IramunoL 76, 724-729. Tovey, E. R., Chapman, M. D., Wells, C. W. and Platts-Mills, T. A. (1981) The distribution of dust mite allergen in the houses of patients with asthma, Am. Rev. Respir. D/s. 124, 630-635.
0160-4120/86$3.00 + .00 Copyright©1986Pergamon Journals Ltd.
INDOOR ALLERGENS: IDENTIRCATION AND QUANTIFICATION Charles E. Reed and Mark C. Swanson Mayo Clinic, Rochester, Minnesota55905 USA (Received 26 February 1985; Accepted 4 November 1985) A large number of allergens occur in the air of the home and many work sites. Almost any organic dust or volatile chemical reactive with proteins can cause allergic respiratorydisease: allergic rhinitis, asthma, and hypersensitivitypneumonitis (extrinsic allergic alveolitis). If the exposure continues several years after the disease begins there may be permanent disability, so recognition and control of exposure are important. Techniques now exist to sample the particulate antigens suspended in the air and assay them by sensitive immunochemicalmethods.
The Allergens
Introduction The various allergens each arise from particular conditions, so the type and amount o f allergen in the air depends on the circumstances at the site. M a n y allergens are products o f growing organisms; each o f these organisms has its own habitat and conditions that favor its growth. Even in dwellings allergens vary with the construction, furnishings, climate, and season, and with various unique conditions within the building. At the work site the list o f occupational allergens is almost as long as the list o f occupations, for virtually any vapor or aerosolized mist that contains proteins or low molecular weight molecules that can react covalently with proteins can sensitize some o f the workers that are exposed. Most o f the allergens that have been characterized chemically are highly soluble glycoproteins with molecular weights o f 10,000 to 100,000 daltons. In general, for sensitization to occur the antigen must be present in the air in relatively high concentrations and for a rather prolonged period o f time. Once sensitization has occurred, however, a brief minute exposure m a y suffice to elicit an allergic reaction. Particle size is another important factor in allergic reactions. Large particles 10 to 50 ~ m mean mass aerodynamic diameter impact in the nose; optimum size for intrathoracic airway deposition is 1 to 10 ~m; and for deposition in the terminal airways is less than
Household O f the allergens that arise within the home, pyroglyphid mites o f the genus Dermatophagoides are the most widespread (Spieksma et al., 1969; Sinha and van Bronswijk, 1971). These mites, whose food source is human and other animal epidermal scales, have a worldwide distribution, but because they require high humidity they thrive in some climates and are less important in others. At one time it was thought that D. pteronyssinus was the most important house dust mite in Europe and D. farinae in North America, but it is now known that the humidity in the particular house is the determining feature. D. farinae tolerates slightly lower humidity. Allergic disease from house dust mites is most frequent in marine West Coast, Mediterranean, and tropical climates where mild humid winters provide the optimum conditions for these mites to grow. Mattresses and bedding, because o f moisture from the sleeper, and carpets because the floor is cooler and humidity higher, are their main habitats. Mites are more c o m m o n on the ground floor than upper stories and are rare in hotels. The homes o f patients who have asthma associated with house dust allergy are more humid and have more mites than control homes in the same community (Korsgaard, 1983).
1 p.m.
115
116 Studies in Ohio, which has a continental climate with warm humid summers and cold dry winters, show that the numbers of live mites is at a maximum during the summer when windows are open and ventilation is good. In the winter the humidity indoors drops and the mites die (Arlian et al., 1982). It seems that house dust allergy in colder climates is most important in the fall, but in milder climates symptoms change little with the seasons. Mites are too small to be seen with the naked eye, but far too large to become airborne. The major source of respirable dust particles seems to be fecal pellets which are of a size to be efficiently filtered in the nose (Tovey et al., 1981). Our own more recent studies indicate that more than one-half of mite antigen is in particles less than 5/~m, a size that can readily reach the lungs (Swanson et al., 1985). Pets often cause respiratory allergy. Cats, being the most frequent offender, have received the most study. The main antigen, called Cat-1, is an important component of saliva, though small amounts can be found in other body fluids (Bloch et al., 1974). The antigen becomes airborne in 1 to 10 p.m particles presumably after it dries and flakes off the fur (Swanson et al., 1985). The antigen from dogs has not been characterized as thoroughly as cats, although it appears to be similar (Hoffman, 1980). Other pets, such as mice, guinea pigs, gerbils and hamsters also shed allergens and we have found mouse urinary protein in some dwellings in higher concentrations than in research laboratories where it causes occupational respiratory allergy. Feathers have long been considered to be an important antigen in the home, but it now appears that the symptoms and positive skin tests arise more often from mites growing in pillows and bedding rather than bird proteins. Hypersensitivity pneumonitis associated with the hobby of keeping pigeons is the most common illness from exposure to bird antigens. Occasionally, other birds are responsible. Parakeets (budgerigars) can cause an especially serious problem because the disease onset is slow and insidious and may have progressed to pulmonary fibrosis before diagnosis. Pigeon antigens get into the air from the droppings, but their original source is serum proteins secreted into the gut (Barboriak et al., 1969). Insect antigens are highly allergenic, and cockroaches are an important cause of asthma, especially in inner city homes of the lower socioeconomic class (Homberger et al., 1979; Colten et al., 1977). Occupational asthma from insects is common in entomology laboratories. Many authors mention molds as an important indoor allergen, most of the molds cultured indoors have entered from outdoors. In unusual conditions where moisture and nutrients provide the necessary habitat, a mold can flourish sufficiently to cause allergic dis-
C.E. Reedand M. C. Swanson ease (Mathews and Soloman, 1983; Solomon, 1975). In such cases the mold is obvious, but house plants are not a quantitatively significant source of allergenic molds (Berge et al., 1982). On the other hand, microorganisms growing in home humidifiers, air conditioners, and heating systems occasionally do cause asthma or hypersensitivity pneumonitis (Burke et ai., 1977; Banaszak et al., 1970; Fink et al., 1971a, 1971b). This source of indoor allergens is more important in factories and large office buildings (Reed et al., 1983).
Occupational
In his recent review of occupational asthma, Parkes (1982) includes an up-to-date listing of the antigens. Only the more common ones are mentioned in Table 1, a complete listing is beyond the scope of this article. Additional antigens are being recognized not only in new industrial processes, but in old established occupations as well. For example, several groups of investigators have found that glycophageous storage mites are the chief source of antigens responsible for asthma after exposure to hay or grain dust (Cherniack et al., 1974; Agha and Gnanasakthy, 1981; Engstrom et al., 1982). Urinary proteins are the major antigen responsible for asthma and rhinitis from working with laboratory mice, rats and guinea pigs (Longbottom et al., 1977, Swanson et al., 1983). Of the many wood dusts that cause asthma, the most thoroughly studied is western red cedar, Thuja plicata (Chan-Yeung, 1982). Plicatic acid, a low molecular weight substance isolated from the wood, reproduces the airway obstruction, but the mechanism of the obstruction may or may not involve IgE or any other immunological reaction. Although most small highly reactive molecules act as haptens and evoke an IgE reaction, the diisocyanates have not yet been proved to act in this way, and may cause asthma through some other mechanism, possibly by reacting with cell surface receptors (Bernstein, 1982; Butcher et al., 1977). The complexity of the immunological events that occur after inhalation of highly reactive molecules has been illuminated by studies of workers exposed to trimellitic anhydride (Patterson et al., 1982). Not all agents suspected of being airborne allergens turn out to be so. Our studies of asthmatic patients exposed to formaldehyde gas failed to confirm that it caused airway obstruction (Frigas et al., 1984). Sometimes the antigen causing an occupational allergy is not the obvious one. For example, workers in the coffee industry may have asthma not only to green coffee bean dust but also from castor bean dust remaining in the burlap sacks that had previously been used to ship castor beans (Butcher et al., 1978; Johansson et al., 1982).
Indoor allergens
117 Table 1. Indoor allergens.
1. Household dwellings A. House dust mite B. Pets C. Cockroach D. Molds
2. Agricultural and food processing A. Grain dust (? storage mites) B. Moldy hay, silage or bedding C. Bagasse D. Soy, castor, coffee beans E. Sunflower seed, cottonseed, flaxseed F. Wheat flour, rye flour, buckwheat G. Papain H. Shellfish, fish I. Mold on cheese (Penicillium) 3. Woodworking A. Western red cedar B. California redwood C. Maple bark (Cryptostroma corticale) D. Moldy sawdust (both molds and Thermophilic actinomycetes) E. Tropical hardwoods 4. Chemical industry A. Plastics (e.g., diisocyanates, trimellitic anhydride) B. Metals (e.g., nickel, platinum)
C. Pharmaceuticals D. Detergents (Bacillus subtilis enzymes) 5. Textileindustry A. Byssinosis(cotton bract dust) B. Cold water spray air conditioners 6. Cosmetics A. Hair dyes B. Bleaches 7. Laboratory animals A. Rodent urine B. Insects 8. Bird raising A. Pigeons B. Parakeets (Budgerigars)
9. Air conditioners A. Thermophilic actinomycetes
B. Chilled water mist (humidifier fever)
Measurement of Antigens in Indoor Air Quantification o f indoor air pollutants is necessary to assess their importance and to follow the efficacy o f actions taken to control their exposure. Traditional methods o f quantifying allergens in the air depended on counting morphologically identifiable particles like pollen grains or culturing viable organisms like molds. Only recently have methods become available for measuring the amorphous nonviable antigens that are important indoors. Well-standardized techniques have
long existed to measure total particulate solids and many volatile chemicals. These same principles and sampling equipment can be adapted to the measurement o f levels o f antigens in the indoor air and to determine their particle size. T o date application o f these principles has been limited. Clark et aL (1976) found a correlation between the numers o f particles 2 #m and less in diameter in the air after housecleaning and the reduction in peak flow rates o f the children with house dust induced asthma. Chapman et al. 0 9 8 3 ) were unable to detect house dust mite antigen in the air o f undisturbed rooms, but did find antigen during domestic activity. Using a cascade impactor they found that 80% o f the airborne antigen was associated with particles greater than l 0 ~ m in diameter. Some o f these particles had the appearance o f mite feces. Using the same methods, Carswell et al. (1983) estimated the dose of house dust mite antigen inhaled by a 1-month old infant and concluded that it is not sufficient to sensitize. Our studies o f airborne antigens began in 1977 as part o f an investigation o f an outbreak o f hypersensitivity pneumonitis from a contaminanted chilled water spray wash air conditioning system (Reed et al., 1983). Slime growing in the chilled water reservoirs contained an array o f antigens that reacted with IgG antibodies in the serum o f the affected workers and also elicited a positive inhalation challenge test. By appropriate immunochemical procedures it is possible to measure both the antibody and the antigen. To measure airborne antigen at work sites within the plant, particles larger than 0.3 ~Lm were collected on a 20 x 25 cm fiberglass filter paper sheet using a high-volume air sampler (GMS-3210 Accu-Vol, General Metal Works, Cleves, OH). The antigens were eluted from the filter paper by descending chromatography into a collecting beaker. After dialysis and lyophilization the antigens were assayed by a radioimmunoassay inhibition technique that e m p l o y e d antiserum from affected workers. We found levels o f antigen in the air at the work site o f 0.5 to 15 ~m/m 3. Effective actions reduced the antigen in the water and as a result the level of antigen in the air declined gradually over the next 2 yr to levels o f 0.001 to 0.0001 ~Lm/m3, values equal to or less than levels measurable in the outdoor air of the community. This same technique with modifications can be used to measure any antigen, provided that an antigen reference standard exists and that serum containing either IgG or IgE antibody is at hand. Furthermore, an Andersen cascade impaction attachment is available for the Accu-Vol sampler (Andersen Samplers Inc., Atlanta, GA), so that the amount o f antigen in various particle sizes can be determined. Thus, we now have the technology to investigate many interesting questions. With several samplers operating simultaneously, several sites can be compared to determine
C.E. Reed and M. C. Swanson
118
DISTRIBUTION OF ,~LIRRGEN ACTMTY IN AIRBORNE PARTICLES OF DEFINED SIZES STAGE 1 >4.1 u
X TOTAL ~
STAGE 2 <<..1 u>2.3u
STAGE 3 <2.3u>1.4.u
STAGES 4J¢5 <1.4u
ACTIVITY
60
50
40
30
20
10
~
; / / / V////] / / / / V////J / i / / V//I/J / ,, / I V / / / A ///i
~ I I I
.. - . . . . . i Y / / / / V / Z / / J 1. - . . - . . iF / / " "~ V / / I / ] I'. - - ' . " Y " / / / V I / / / J I ' . - ' . "." ~Y i / i / V / / / / ~ .....i///
CAT /M.LERGEN MITE ALLERGEN SAMPLES BY ACCU-VOL wl'n-I ANDERSEN CASCADE IMPACTION HEAD
Fig. I.
differences in concentration at different places. The same site can be sampled sequentially to determine different concentrations at different times or to test the effect of interventions undertaken to alter the concentration. We have measured mouse urinary proteins and mouse pelt proteins in the air of an animal quarters, in an immunology laboratory where there were five mice, and in the same laboratory over the weekend (Agarwal e t a l . , 1982). Airborne antigen content varied from 1.8 to 825 p.g/m3 depending on the site and degree of work activity in the room. Thin layer electrofocusing of the air sample filter eluate showed bands that were common to those produced by mouse urine, mouse pelt extract and mouse serum albumin. No single one of their sources contained all the bands of the filter eluate. Studies with guinea pig allergens gave similar results, but guinea pig urine proteins were the dominant antigen (Swanson, 1983). Most of the antigen occurred in particles larger than 5 p.m or smaller than 0.8 p.m in diameter. In a Rochester, MN, home with three cats, we found that most of the cat antigen was contained in particles less than 5 p.m (Table 2). Also, in contrast to the studies of Chapman e t a l . (1983) we found airborne house dust mite antigen was also chiefly in particles less than 4 p,m, too small to be associated with mite fecal pellets. The concentration of both cat and mite antigen greatly increased for 20 min after making a bed where the cat often slept. Rather surprisingly,
the particle size of the antigen was not much different. The antigen was predominantly in particles less than 5 p.m. The Accu-Vol sampler is not suitable for home sampiing. It is too noisy. Also, sampling the relatively small finite volume of air in a home requires either intermittent sampling or continuous sampling at flow rates that will have only a negligible cleaning effect on the total volume of air being sampled. We have designed quiet samplers that operate in the range of 1 to 6 L/sec (Swanson e t al., 1984). Substitution of Gortex ® for fiberglass improves the efficacy of elution of the allergen and avoids the necessity for lyophilization which may destroy labile antigens. However, the sensitivity of the assay techniques will not permit sampling volumes much smaller than 50 m 3. Duration of sampling depends on the concentration of the antigen under consideration. Aeroallergen
quantitation
Airborne allergen levels from middle class single family dwellings in Rochester, MN, and crowded apartments in Harlem, NY, provide contrasting information about the prevalence and relation concentrations of various aeroallergens (Table 3). In Rochester, dwelling 1 had three pet cats, dwelling 4 had two, and dwelling 3 had one pet cat. Dwelling 8 had three pet guinea pigs, and dwelling 9 had one. Thus, the amount of animal antigen in the air is proportional to the number of animals in the house.
Indoor allergens
119 Table 2. Duration of suspended antigens associated with particles of various sizes in the air after making a bed. Antigen Concentration
(pg protein/m') Mite
Cat
Particle Size
5 rain
20 min
24 h
20 rain
24 h
Larger than 4.1 ttm <4.1 t~m >2.3 ttm <2.3 t~m > 1.4 ~,m < 1.4 t~m >0.8 tan Smaller than 0.8 t~m
83,920 162,790 176,420 218,490 94,470
17,520 63,280 24,170 44,510 40,430
240 520 220 470 290
14,460 9,110 3,170 7,720 15,090
6,550 6,430 4,460 5,510 14,380
The concentration o f house dust mite antigen in the air was similar in these homes as was the concentration o f cat in homes with cats. However, the concentration o f cockroach and m o u s e urinary protein was m u c h higher in the air o f lower socioeconomic homes. In some o f these tenements the concentration o f mouse urinary protein was similar to concentration in the air o f a laboratory where there were several mice and where researchers allergic had symptoms.
Control of Indoor Allergens Control o f exposure to indoor allergens offers the most effective strategy for treating the respiratory allergic disease they cause. Prompt accurate diagnosis is the cornerstone o f success. Promptness is important because continued exposure in cases o f asthma leads to airway hyperirritability and airway obstruction that can persist months or years after the exposure ceases (Bernstein, 1982). Continued exposure in cases o f hypersensitivity pneumonitis leads to p u l m o n a r y fibrosis and permanent p u l m o n a r y disability (Fink et al., 1982). A c c u r a c y is equally important. Just as a missed
diagnosis can be tragic, an error in the other direction can also be harmful. Mistaken advice to change occupation or home can seriously disrupt a person's life by economic loss or by useless restrictions on his activity and place unnecessary burdens on his family as well. Each antigen has its own particular means o f control. Sometimes identification o f the antigen allows simple direct action such as removing a cat from the house, but usually control is more difficult. Improved ventilation m a y suffice, but in cold climates energy costs for heating a large flow of air may be prohibitively expensive. For microbial antigens, it is often possible to improve ventilation in a damp environment that is responsible for promoting growth, or to add an antimicrobial chemical to contaminated chilled water air conditioning systems. Cleaning is quite helpful when the contamination is obvious. Cleaning not only removes antigen but, clean, uncluttered buildings provide fewer niches where nutrients and humidity allow microbes or arthropods to grow. In occupational exposures engineering changes in plant design and materials handling are effective. For example, toluene
Table 3. Indoor allergen concentrations (picograms of protein per cubic meter). Dwelling Rochester 1
Mite
Cat
2 3 4 5 6 7 8
1610 370 1600 2600 4090 5570 2790 NDa
92,000 < 1,000 17,000 51,000 ND ND ND < 1,000
9
ND
<,1000
2400 3700 3140 2160 3220
5,110 6,290 55,900 13,150 14,680
Harlem 1 2 3
4 5
NDa = not determined.
Roach
Mouse Urine
Guinea Pig Urine
< 1,000
<3
< 1,000
ND ND ND ND ND < 1,000 ND
<3 <3 <3 <3 <3 <3 <3
ND
<3
< 1,000 < 1,000 < 1,000 < 1,000 ND ND 495,000 118,000
2960 430 230 1240 610
ND ND ND ND ND
20,010 16,240 25,100 42,480 43,430
120
diisocyanate spills can be reduced by keeping the chemical contained at all times. Monitoring the concentration o f antigen in the air is useful in order to follow the effectiveness of control measures in those cases where eradication of exposure is not feasible. In some occupational exposures such as farming, control of the antigen at the source is impossible. Instead, personal protective equipment is desirable. Filter masks have not proved to be as satisfactory as laminar flow helmets that provide a curtain of filtered air in front of the face. Occasionally, as a last resort, the only means of controlling the disease is a change of occupation.
References Agha, M. and Gnanasakthy, A. (1981) A cluster of analysis of the effects of storage mites on allergens in relation to certain occupations and living conditions, Clin. Allergy 11,499-504. Agarwal, M. K., Dahlberg, M. E., Twiggs, J. T. and Yunginger, J. W. (1982) Immunochemical measurement of airborne mouse allergens in a laboratory animal facility, J. Allergy Clin. lmmunol. 69, 522-526. Arlian, L. G., Bernstein, I. L. and Gallagher, J. J. (1982) The prevalence of house dust mites, Dermatophagoides spp, and associated environmental conditions in homes in Ohio, J. Allergy Clin. lmmunol. 69, 527-532. Banaszak, E. F., Thiede, W. H. and Fink, J. N. (1970) Hypersensitivity pneumonitis due to contamination of an air conditioner, New Engl. J. Med. 283, 271. Barboriak, J. J., Edwards, J. H. and Fink, J. N. (1969) Excretions of pigeon serum proteins in pigeon droppings, Proc. Soc. Exp. Biol. Med. 132, 907. Bernstein, I. L. (1982) Isocyanate-induced pulmonary diseases: A current perspective, J. Allergy Clin. lmmunol. 70, 24-31. Berge, H. A., Boise, J. R. and Solomon, W. R. (1980) Microbial prevalence in domestic humidifiers, Appl. Environ, Microbiol. 39, 840. Berge, H. A., Solomon, W. R. and Mulenberg, M. S. (1982) Evaluation of indoor plantings as allergen exposure sources, J. Allergy Clin. lmmunol. 76, 101-108. Bloch, K. J., Lowell, F. C. and Ohman, J. L., Jr. (1974) Allergens of mammalian origin. III. Properties of a major feline allergen, J. lmmunol. 113, 1668. Burke, G. W., Carrington, C. B., Fink, J. N., Gaensler, E. A. and Strauss, R. (1977) Allergic alveolitis caused by home humidifiers. Unusual clinical features and electron microscopic findings. J. Am. Med. Soc. 238, 2705-2708. Butcher, B. T., Davies, R. J., O'Neil, C. E. and Salvaggio, J. E. (1977) The in vitro effect of toluene diisocyanate on lymphocyte cyclic adenosine monophosphate production by isoproterenol, prostaglandin, and histamine, J. Allergy Clin. lmmunol. 60, 223. Butcher, B. T., Karr, R. M., Lehrer, S. B., and Salvaggio, J. E. (1978) Coffee worker's asthma. A clinical appraisal using the radioallergosorbent test, J. Allergy Clin. lmmunol. 62, 143-148. Carswell, F., Clark, J., Platts-Mills, T. A. and Robinson, P. (1983) The dose of house dust mite antigen (PI) inhaled by infants aged one month, Ann. Allergy 51,539-542. Chan-Yeung, M. (1982) Immunologic and nonimmunologic mechanisms in asthma due to western red cedar (Thuja plicata), J. Allergy Clin. lmmunol. 70, 32-37. Chapman, M. D., Piatts-Mills, T. A. E. and Tovey, E. R. (1981)
C.E. Reed and M. C. Swanson Mite faeces are a major source of house dust allergens, Nature 289, 592-593. Cherniack, R. M., Tse, K. S. and Warren, P. (1974) Hypersensitivity reactions to grain dust, J. Allergy Clin. lmmunol. 53, 139-149. Clark, R. P., Cordon-Nesbitt, D. C., Malka, S., Preston, T. D. and Sinclair, L. (1976) The size of airborne dust particles precipitating bronchospasm in house dust sensitive children, J. Hygiene (Camb.) 77, 321-325. Colten, H. R., Picone, F. J., So, J., Strunk, R. S. and Twarog, F. J. (1977) Immediate hypersensitivity to cockroach. Isolation and purification of the major antigens, J. Allergy Clin. ImmunoI. 59, 154-160. Engstrom, B., Hillerdal, G,, Johansson, S. G. O., Wiren, A. and Zetterstrom, O. (1982) Mites living in hay: An important allergen source?, Allergy 37, 475-479. Fink, J. N., Resnick, A. J. and Salvaggio, J. E. (1971a) Presence of themophilic retinomycetes in residential heating systems, Appl Microbiol. 22, 730. Fink, J. N., Banaszak, E. F., Thiede, W. H. and Barboriak, J. J. (1971b) Interstitial pneumonitis due to hypersensitivity to an organism contaminating a heating system, Ann. Intern. Med. 74, 80. Frigas, E,, FiUey, W. V., and Reed C. E. (1984) Bronchial challenge with formaldehyde gas: Lack of bronchoconstriction in 13 patients suspected of formaldehyde-induced asthma, Mayo Clin. Proc. 59, 295-299. Hoffman, D. R. (1980) Dog and cat allergens: Urinary proteins or dander proteins?, Ann. Allergy 45, 205-206. Homburger, H., Kang, B., Vellody, D. and Yunginger, J, W. (1979) Cockroach cause of allergic asthma. Its specificity and immunologic profile, J. Allergy Clin. lmmunol. 63, 80-86. Johansson, S. G., Osterman, K. and Zetterstrom, O. (1982) Coffee worker's allergy, Allergy 37, 313-322. Korsgaard, J. (1983) Mite asthma and residency. A case-control study on the impact of exposure to house-dust mites in dwellings, Am. Rev. Respir. Dis. 128, 231-235. Longbottom, J. L., Newman-Taylor, A. and Pepys, J. (1977) Respiratory allergy to urine proteins of rats and mice, Lancet 2, 847-849. Mathews, K. P. and Solomon, W. R. (1983) Aerobiology and inhalant allergens, in Allergy: Principles and Practice, 2nd ed., E. Middleton, C. E. Reed, and E. F. Ellis, eds., pp. 1143-1202. C. V. Mosby Company, St. Louis, MO. Parkes, W. R. (1982) Occupational Lung Disorders, 2nd ed., pp. 416-422. Butterworths, London. Patterson, R., Pruzanski, J. J., and Zeiss, C. R. (1982) Immunology and immunopathology of trimellitic anhydride pulmonary reactions, J. Allergy Clin. lmmunol. 70, 19-23. Reed, C. E., Swanson, M. C., Lopez, M., Ford, A. M., Major, J., Witmer, W. B., and Valdes, T. B. (1983) Measurement of IgG antibody and airborne antigen to control an industrial outbreak of hypersensitivity pneumonitis, J. Occup. Med. 25, 207-210. Sinha, R. N. and van Bronswijk, J. E. (1971) Pyroglyphid mites (Acari) and house dust allergy, J. Allergy Clin. lmmunol. 47, 31-52. Solomon, W. R. (1975) Assessing fungus prevalence in domestic interiors, J. Allergy Clin. lmmunol. 56, 235. Spieksma, F. T. M., Varekamp, H., and Voorhorst, R. (1969) House Dust Atopy and the House Dust Mite. Stafeus, Leiden. Swanson, M. C., Agarwal, M. K., Yunginger, J. W. and Reed, C. E. (1984) Guinea pig derived allergens: Clinicoimmunologic studies, characterization, airborne quantitations and size distribution, Am. Rev. Resp. Dis. 129, 844-849. Swanson, M. C., Agarwal, M. K., and Reed, C. E. (1985) An immunochemical approach to indoor aeroallergen quantitation with a new volumetric air sampler. Studies with mite, roach, cat, mouse, and guinea pig antigens, J. Allergy Clin. IramunoL 76, 724-729. Tovey, E. R., Chapman, M. D., Wells, C. W. and Platts-Mills, T. A. (1981) The distribution of dust mite allergen in the houses of patients with asthma, Am. Rev. Respir. D/s. 124, 630-635.