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What we do and do not know about mold allergy and asthma
Editorial What we do and do not know about mold allergy and asthma
For more than 60 years molds have been generally considered to be important causes of asthma, but mold allergy has been the most difficult aspect of aeroallergy to investigate. Even though we have made steady progress in solving problems surrounding identification of mold allergens, diagnosis in individual patients, and treatment, many questions remain unanswered.’ The article of Licorish et al. in this issue of the JOURNAL, page 819, provides confirmation that inhalation of Alternaria or Penicillium spores can cause asthma in mold-sensitive patients.’ Their article provides an opportunity to consider the current status of the field and to speculate about where new research is likely to lead. Pratt3 in 1941 suggested that spores contained most of the antigen but cautioned, “However, the final answer cannot be given until methods are available for standardizing the atopic content of Alternaria extracts.““. 4 Such methods are now available.s-7 As Licorish et al.” point out, the failure of pollen grains to penetrate the intrathoracic airways and provoke local allergic reactions there cast doubt on the concept that particles as large as typical Alternaria spores could cause asthma. The observation that AIternaria spores do provoke positive bronchial challenges presumably is explained by the fact that some spores are quite small and that the snowshoe-shaped Alternaria spore has different aerodynamic properties than the billiard ball-shaped pollen grain that keeps it from impacting in the upper airway. Any final doubt that mold spores can cause asthma was resolved by the authors’ finding that the number of spores required to provoke the reaction in the laboratory was similar to the number that might be inhaled in a 24-hour period of natural exposure. Identification of mold aeroallergens is still the main barrier to progress. Without detailed information about the kind and amount of antigen in the air at different times and places and without reliable standard allergen extracts for skin or bronchial provocation testing, it is not possible to correlate signs and symptoms of asthma with exposure. Many difficulties surround identification and quantification of mold allergens in the air. The traditional techniques of culture
and microscopic identification both have limitations.# Many fungi have very specific growth requirements that prevent culture in the laboratory. Some, like rusts or smuts, may parasitize only a single species of plant. Other fastidious basidiomycetes or ascomycetes grow only in unique ecologic environments. If their spores have a recognizable morphology, their abundance can be estimated with the counting techniques used for pollens, but unfortunately, not all have discrete identifiable morphology. Many of them are spheres of 3 to 6 pm in diameter that appear to be pretty much alike. Culture methods may elicit misleading values even for molds like Alternaria that grow well. Not all spores germinate. Spores of some molds like Cladosporium may occur in clumps so that the number of colonies does not always represent the number of spores. Furthermore, mold antigen may be airborne in amorphous particles; enumeration of spores may underestimate the total amount of antigen in the air. New immunochemical assay techniques coupled with quantitative high-volume air filtration sampling avoid the difficulties of culture or morphologic identification and offer the additional advantage of determining the size of amorphous allergen particles. For example, Agarwal et a1.9,‘Ofound that even though the amount of Alternaria antigen measured immunochemically correlated very well with spore counts, considerable antigen occurred in particles smaller than spores, a situation quite analogous to the finding that about half of the ragweed antigen in the air was associated with particles or droplets smaller than pollen grains.‘.” Immunochemical assay methods have limitations of their own. They require standard reference antigen preparations and antisera that are specific to the particular mold being assayed. In addition, they cannot distinguish between sources of cross-reacting allergens. Hence, combination of culture, microscopic counts, and immunochemical aeroallergen assay techniques coupled with field surveys are necessary to define the amount, particle size. and distribution of a particular fungal allergen. It is now certain that mold spores can provoke asthma. The questions that remain are whether spores are the only major source of air773
774 Reed borne allergen, which species of molds can be responsible, and how important are mold allergens compared to other aeroallergens. As they grow, molds secrete digestive enzymes and other antigens into the substrate.” Ii In the case of allergic bronchopulmonary aspergillosis where the mold germinates and grows within the body. these “metabolic” antigens are much more relevant in causing the disease than spore antigens. and Aspergillus culture filtrates contain many times more antigen than mat or spore extracts. Whether or not similar “metabolic” antigens secreted in the process of growth in the field and carried on amorphous dust particles contributes to causing asthma from molds like Altertuwic~ and Penicillium remains to be determined. With basidiomycetes and ascomycetes it is conceivable that the total amount of antigenic material in the air may be much greater than the amount in their spores. As Pratt so prophetically said. progress had to wait for standardized allergen preparations. Mold extracts pose even more difficult problems of standardization than do pollens or animal allergens. Many variables determine the allergen content of mold extracts. lmportant variables include composition of the culture medium, surface or submerged growth. duration, illumination, aeration, and temperature of the culture; strain of the organism. number of subcultures the strain had undergone since isolation from its natural habitat, and whether the extract is prepared from the spores, mycelial mat, culture medium. or a combination. A World Health Organization Committee is developing international reference standards for allergens including molds, but so far only timothy, short ragweed, and Dermatophagoides pterotgxsinus are available. Cladosporium and Alrernuria are being considered. The Bureau of Biologics Research and Review of the Food and Drug Administration is encouraging U.S. standards for molds and has accepted reference preparations for Alternariu and listilago. The American Type Culture Collection now has specimens of many molds freshly isolated from the air that can serve as reliable sources for allergen preparations. It would appear appropriate for investigators studying fungi to prepare sufficient amounts of extracts so that lyophilized aliquots will be available for future reference. Although molds can cause asthma, it is not clear how often they do. In the Midwest. Alternaria appears to be quite important. For example. in Madison. Wisconsin, I found that in a series of 100 consecutive patients with allergic asthma, skin tests were positive to Alternaria in more than 80% and to ragweed in 70%. and skin tests positive to cat were third at 45%. Most of these patients had asthma symptoms before
.i ALLERGY
i:.LIN iMMUNOi.. ‘I’CFMBER ,985
and after the ragweed season (about August Ii) t(; September 20) but during the time of year-,~~irc~rrc;~,r~ spore counts are high (July through Octohcrj. In iii!) consecutive patients with only allergic rltinitl\i. as Salvaggio et al.” suggested, other fungi Irks: ha5 idiomycetes might be important. Of course. ohscrvations on patients in one climate do nc.jt apply t(g patients in other climates. In addition to fungi that grow outdoor>. mold, growing indoors have been suspected a’~ aeroallrr gens. With use of indoor air samplers and immunochemical techniques. we find. as Licorish ct ai. did with the use of cultures, that large amounts of Altrrnaria allergen have blown in from outside. The stud& of Burge et al. ITindicate that in Midwest homes spores from molds growing indoors are not abundant and that house plants do not introducc a burden of mold ailergens into the indoor air. Molds require rnoihturt: and will not grow unless the humidity consistently exceeds 70%. Again. observations in one climate do not necessarily apply to other climates. indoor molds may be more important in more humid climares. Occasionally. in bathrooms or basements, ;I persistcni damp area may support enough mold growth in othcrwise dry houses to cause disease. We need tir bc alert to the possibility that occasional buildings or homrs may become sufficiently contaminated with mold 10 cause asthma. New buildings are being t.onstructcd tightly to avoid air leaks in order to save heating cost>. and as a result indoor humidity increases. iJIb<). indoor aeroallergens accumulate when the air in a tight bulkiing exchanges only once every 2 hours rather than the five times an hour typical of older homch Treatment of mold allergy also presents unsolved problems. Control of the source of exposure IS possible in contaminated buildings where building repair. improved ventilation, and removing cold mist humidifiers is the preferred treatment. But lest UC: place unnecessary financial burdens on patients or their employers by recommending unnecessary environmental changes. we must demand strict criteria for this di,agnosis. The minimum criteria should be that spores or allergen be abundant in the indoor air, that the patient have IgE antibody to the same allergen. and that the patient have increased symptoms on exposure to it. Air-conditioning reduces exposure to outdoor molds.‘” It probably is useful in reducing symptoms, but no controlled trials are available. Midwest Alter-
VOLUME 76 NUMBER 6
What we do and do not know about mold allergy
nariu-sensitive patients can benefit from moving to the relatively mold-free climate of western Oregon and Washington, but such a move should be recommended in only exceptional circumstances. As yet, no controlled clinical trials of mold immunotherapy for asthma have been published. Based on my experience with the patients allergic to Alternariu mentioned above, I believe that immunotherapy with Alternuria is less satisfactory than immunotherapy with ragweed. Although it evokes an IgG-antibody response, systemic reactions are more frequent, and more patients have continued severe symptoms. In my opinion, there is no basis for prescribing mold immunotherapy solely because of weak positive intradermal skin tests. Treatment should be reserved for those patients with an unequivocal specific diagnosis that meets criteria analogous to those outlined above. Division
of Internal
Charles E. Reed, M.D. Medicine and Allergic Diseases Mayo Clinic and Foundation 200 First Street, SW Rochester, MN 55901
I Salvaggio J, Aukrust L: Mold-induced asthma. J ALLERGY CLIN IMMKJNOL 68:327. 1981 2. Licorish K, Novey HS, Kozak P, et al: Role of Affernaria and fenicillium spores in the pathogenesis of asthma. J ALLERGY CLIN IMMUNOL 76:819. 1985 3. Pratt HN: Species specificity of Alternaria in asthma and hay fever. J ALLERGY 12:431, 1941 4. Pratt HN. Crossman R: The comparative atopic activity of Alternariu spores and mycelium. J ALLERGY 13:227. 1942 5. Yunginger JW, Jones RT, Gleich J: Studies on Alrernaria al-
775
lergens. II: Measurement of the relative potency of commercial Alfernaria extracts by the direct RAST and by RAST inhibition. J ALLERGY CLIN IMMUNOL .58:405. 1976 6. Lowenstein H, Aukrust L. Grovensen S: Cladosporium herbarum extract characterized by means of quantitative immu-
noelectrophoretic methods and special attention to immediatetype allergy. Int Arch Allergy Appl Immunol 55: I, 1977 7. Yunginger JY, Jones RT. Nesheim ME. et al: Studies on Alrernariu allergens. III: Isolation of a major allergenic fraction (ALT-1). J ALLERGY CLIN IMMUNOL 66: 138. 1980 8. Solomon WR: Sampling techniques for airborne fungi. In Aldoory Y, Domson JF. editors: Mould allergy. Philadelphia, 1984, Lea & Febiger, p 41 9. Agarwal MK. Yunginger JW. Swanson MC, et al: An immunochemical method to measure atmospheric allergens. J ALLERGY CLIN IMMUNOL 68:194,
1981
JO. Agarwal MK, Swanson MC, Reed CE, et al: Airborne ragweed allergens: association with various particle sizes and short ragweed plant parts. J ALLERGY CLIN IMMUNOL 74:687. 1984 11. Habenicht HA, Burge HA, Muilenberg ML. Solomon WR: Allergen carriage by atmospheric aerosol. Ii: Ragweed-pollen determinants in submicronic atmospheric fractions. J ALLERGY CLIN IMMUNOL 74:64,
1984
12. Longbottom JL, Pepys J: Pulmonary aspergillosis. Diagnostic and immunologic significance of antigens and C-substance in Asperpillusfumigatus. J Path01 Bacterial 88: 141, 1964 13. Reed CE: Variability of antigenicity of Aspergillus fumigatus. J ALLERGY CLIN IMMUNOL 61:227,
REFERENCES
and asthma
1978
14. Salvaggio J. Seabury J. Schoenhardt E: New Orleans asthma. V. Relationship between Charity Hospital asthma admission rates, semiquantitative pollen and fungal spore counts, and total particulate aerometric sampling data. J ALLERGY CLIN IMMUNOL 48:96,
1971
15. Burge HA, Solomon WR. Mulenberg MS: Evaluation of indoor plantings as allergen exposure sources. J ALLERGY CLIN IMMUNOL 70:101,
1982
16. Solomon WR. Burge HA, Boise JR: Exclusion of particulate allergens by window air conditioners. J ALLERGY CLIN IMMUNOL 65:308.
1980
For more than 60 years molds have been generally considered to be important causes of asthma, but mold allergy has been the most difficult aspect of aeroallergy to investigate. Even though we have made steady progress in solving problems surrounding identification of mold allergens, diagnosis in individual patients, and treatment, many questions remain unanswered.’ The article of Licorish et al. in this issue of the JOURNAL, page 819, provides confirmation that inhalation of Alternaria or Penicillium spores can cause asthma in mold-sensitive patients.’ Their article provides an opportunity to consider the current status of the field and to speculate about where new research is likely to lead. Pratt3 in 1941 suggested that spores contained most of the antigen but cautioned, “However, the final answer cannot be given until methods are available for standardizing the atopic content of Alternaria extracts.““. 4 Such methods are now available.s-7 As Licorish et al.” point out, the failure of pollen grains to penetrate the intrathoracic airways and provoke local allergic reactions there cast doubt on the concept that particles as large as typical Alternaria spores could cause asthma. The observation that AIternaria spores do provoke positive bronchial challenges presumably is explained by the fact that some spores are quite small and that the snowshoe-shaped Alternaria spore has different aerodynamic properties than the billiard ball-shaped pollen grain that keeps it from impacting in the upper airway. Any final doubt that mold spores can cause asthma was resolved by the authors’ finding that the number of spores required to provoke the reaction in the laboratory was similar to the number that might be inhaled in a 24-hour period of natural exposure. Identification of mold aeroallergens is still the main barrier to progress. Without detailed information about the kind and amount of antigen in the air at different times and places and without reliable standard allergen extracts for skin or bronchial provocation testing, it is not possible to correlate signs and symptoms of asthma with exposure. Many difficulties surround identification and quantification of mold allergens in the air. The traditional techniques of culture
and microscopic identification both have limitations.# Many fungi have very specific growth requirements that prevent culture in the laboratory. Some, like rusts or smuts, may parasitize only a single species of plant. Other fastidious basidiomycetes or ascomycetes grow only in unique ecologic environments. If their spores have a recognizable morphology, their abundance can be estimated with the counting techniques used for pollens, but unfortunately, not all have discrete identifiable morphology. Many of them are spheres of 3 to 6 pm in diameter that appear to be pretty much alike. Culture methods may elicit misleading values even for molds like Alternaria that grow well. Not all spores germinate. Spores of some molds like Cladosporium may occur in clumps so that the number of colonies does not always represent the number of spores. Furthermore, mold antigen may be airborne in amorphous particles; enumeration of spores may underestimate the total amount of antigen in the air. New immunochemical assay techniques coupled with quantitative high-volume air filtration sampling avoid the difficulties of culture or morphologic identification and offer the additional advantage of determining the size of amorphous allergen particles. For example, Agarwal et a1.9,‘Ofound that even though the amount of Alternaria antigen measured immunochemically correlated very well with spore counts, considerable antigen occurred in particles smaller than spores, a situation quite analogous to the finding that about half of the ragweed antigen in the air was associated with particles or droplets smaller than pollen grains.‘.” Immunochemical assay methods have limitations of their own. They require standard reference antigen preparations and antisera that are specific to the particular mold being assayed. In addition, they cannot distinguish between sources of cross-reacting allergens. Hence, combination of culture, microscopic counts, and immunochemical aeroallergen assay techniques coupled with field surveys are necessary to define the amount, particle size. and distribution of a particular fungal allergen. It is now certain that mold spores can provoke asthma. The questions that remain are whether spores are the only major source of air773
774 Reed borne allergen, which species of molds can be responsible, and how important are mold allergens compared to other aeroallergens. As they grow, molds secrete digestive enzymes and other antigens into the substrate.” Ii In the case of allergic bronchopulmonary aspergillosis where the mold germinates and grows within the body. these “metabolic” antigens are much more relevant in causing the disease than spore antigens. and Aspergillus culture filtrates contain many times more antigen than mat or spore extracts. Whether or not similar “metabolic” antigens secreted in the process of growth in the field and carried on amorphous dust particles contributes to causing asthma from molds like Altertuwic~ and Penicillium remains to be determined. With basidiomycetes and ascomycetes it is conceivable that the total amount of antigenic material in the air may be much greater than the amount in their spores. As Pratt so prophetically said. progress had to wait for standardized allergen preparations. Mold extracts pose even more difficult problems of standardization than do pollens or animal allergens. Many variables determine the allergen content of mold extracts. lmportant variables include composition of the culture medium, surface or submerged growth. duration, illumination, aeration, and temperature of the culture; strain of the organism. number of subcultures the strain had undergone since isolation from its natural habitat, and whether the extract is prepared from the spores, mycelial mat, culture medium. or a combination. A World Health Organization Committee is developing international reference standards for allergens including molds, but so far only timothy, short ragweed, and Dermatophagoides pterotgxsinus are available. Cladosporium and Alrernuria are being considered. The Bureau of Biologics Research and Review of the Food and Drug Administration is encouraging U.S. standards for molds and has accepted reference preparations for Alternariu and listilago. The American Type Culture Collection now has specimens of many molds freshly isolated from the air that can serve as reliable sources for allergen preparations. It would appear appropriate for investigators studying fungi to prepare sufficient amounts of extracts so that lyophilized aliquots will be available for future reference. Although molds can cause asthma, it is not clear how often they do. In the Midwest. Alternaria appears to be quite important. For example. in Madison. Wisconsin, I found that in a series of 100 consecutive patients with allergic asthma, skin tests were positive to Alternaria in more than 80% and to ragweed in 70%. and skin tests positive to cat were third at 45%. Most of these patients had asthma symptoms before
.i ALLERGY
i:.LIN iMMUNOi.. ‘I’CFMBER ,985
and after the ragweed season (about August Ii) t(; September 20) but during the time of year-,~~irc~rrc;~,r~ spore counts are high (July through Octohcrj. In iii!) consecutive patients with only allergic rltinitl\
VOLUME 76 NUMBER 6
What we do and do not know about mold allergy
nariu-sensitive patients can benefit from moving to the relatively mold-free climate of western Oregon and Washington, but such a move should be recommended in only exceptional circumstances. As yet, no controlled clinical trials of mold immunotherapy for asthma have been published. Based on my experience with the patients allergic to Alternariu mentioned above, I believe that immunotherapy with Alternuria is less satisfactory than immunotherapy with ragweed. Although it evokes an IgG-antibody response, systemic reactions are more frequent, and more patients have continued severe symptoms. In my opinion, there is no basis for prescribing mold immunotherapy solely because of weak positive intradermal skin tests. Treatment should be reserved for those patients with an unequivocal specific diagnosis that meets criteria analogous to those outlined above. Division
of Internal
Charles E. Reed, M.D. Medicine and Allergic Diseases Mayo Clinic and Foundation 200 First Street, SW Rochester, MN 55901
I Salvaggio J, Aukrust L: Mold-induced asthma. J ALLERGY CLIN IMMKJNOL 68:327. 1981 2. Licorish K, Novey HS, Kozak P, et al: Role of Affernaria and fenicillium spores in the pathogenesis of asthma. J ALLERGY CLIN IMMUNOL 76:819. 1985 3. Pratt HN: Species specificity of Alternaria in asthma and hay fever. J ALLERGY 12:431, 1941 4. Pratt HN. Crossman R: The comparative atopic activity of Alternariu spores and mycelium. J ALLERGY 13:227. 1942 5. Yunginger JW, Jones RT, Gleich J: Studies on Alrernaria al-
775
lergens. II: Measurement of the relative potency of commercial Alfernaria extracts by the direct RAST and by RAST inhibition. J ALLERGY CLIN IMMUNOL .58:405. 1976 6. Lowenstein H, Aukrust L. Grovensen S: Cladosporium herbarum extract characterized by means of quantitative immu-
noelectrophoretic methods and special attention to immediatetype allergy. Int Arch Allergy Appl Immunol 55: I, 1977 7. Yunginger JY, Jones RT. Nesheim ME. et al: Studies on Alrernariu allergens. III: Isolation of a major allergenic fraction (ALT-1). J ALLERGY CLIN IMMUNOL 66: 138. 1980 8. Solomon WR: Sampling techniques for airborne fungi. In Aldoory Y, Domson JF. editors: Mould allergy. Philadelphia, 1984, Lea & Febiger, p 41 9. Agarwal MK. Yunginger JW. Swanson MC, et al: An immunochemical method to measure atmospheric allergens. J ALLERGY CLIN IMMUNOL 68:194,
1981
JO. Agarwal MK, Swanson MC, Reed CE, et al: Airborne ragweed allergens: association with various particle sizes and short ragweed plant parts. J ALLERGY CLIN IMMUNOL 74:687. 1984 11. Habenicht HA, Burge HA, Muilenberg ML. Solomon WR: Allergen carriage by atmospheric aerosol. Ii: Ragweed-pollen determinants in submicronic atmospheric fractions. J ALLERGY CLIN IMMUNOL 74:64,
1984
12. Longbottom JL, Pepys J: Pulmonary aspergillosis. Diagnostic and immunologic significance of antigens and C-substance in Asperpillusfumigatus. J Path01 Bacterial 88: 141, 1964 13. Reed CE: Variability of antigenicity of Aspergillus fumigatus. J ALLERGY CLIN IMMUNOL 61:227,
REFERENCES
and asthma
1978
14. Salvaggio J. Seabury J. Schoenhardt E: New Orleans asthma. V. Relationship between Charity Hospital asthma admission rates, semiquantitative pollen and fungal spore counts, and total particulate aerometric sampling data. J ALLERGY CLIN IMMUNOL 48:96,
1971
15. Burge HA, Solomon WR. Mulenberg MS: Evaluation of indoor plantings as allergen exposure sources. J ALLERGY CLIN IMMUNOL 70:101,
1982
16. Solomon WR. Burge HA, Boise JR: Exclusion of particulate allergens by window air conditioners. J ALLERGY CLIN IMMUNOL 65:308.
1980