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Airborne allergens and environmental factors

R. Osdenmoor, M. Lierl

I. Air allergens are fairly large particles of a complex structure (pollen, mold fungi, algae, mites, particles of insects and plants, epidermis of animals), which can cause allergic reactions if they enter the respiratory tract. Actually, the allergen is not the whole particle, but only some of the substances that make up its composition, as a rule, proteins and glycoproteins with a molecular weight of 10,000–40,000. The antigenicity of air allergens is determined by their size, shape, and chemical structure.

A. Origin and particle size of airborne allergens

1. Airborne allergens are particles of biological origin. Some of them (pollen, spores of fungi, algae) can be easily detected in air samples under a microscope, while others (particles of insects, plants, epidermis of animals, fragments of pollen, molds, algae) can be detected only by immunological methods. Hydrocarbons, industrial dust, inorganic crystals and gaseous substances (chlorine, hydrogen sulfide, formaldehyde and gasoline vapors, wood and tobacco smoke, steam formed during cooking) are not antigenic in themselves. However, they change sensitivity to allergens and affect the course of allergic diseases.

2. Particles, distinguishable under a light microscope (diameter 2-60 microns), settle on the mucous membranes of the eyes, nose and throat, without falling into the bronchi. According to one theory, irritating nasopharyngeal receptors, they reflexively cause bronchospasm in exogenous bronchial asthma. According to another point of view, soluble allergens cause bronchospasm, which are separated from particles settled in the nasopharynx and enter the bronchi by inhalation or hematogenous route.

B. Methods for air sampling

1. The gravity method is based on the fact that dense particles suspended in the air settle under the action of gravity. To collect samples by the gravitational method, a Durham sampler is used (see Fig. 3.1). A glass slide coated with glycerin gel is inserted into the device holder, which is prepared as follows: 5 g of gelatin, 40 ml of water, 4 g of phenol are mixed with 195 g of glycerin and heated; during heating, 2 ml of Calberia solution - 5 ml of glycerol, 10 ml of 95% ethanol and 2 drops of a saturated aqueous solution of fuchsin basic are introduced into the gel. The device is left in the air for 24 hours. Particles transferred by the air stream under the influence of gravity settle on a glass slide. The composition and number of particles is determined under a microscope. The results are expressed as the number of particles settled on 1 cm2 in 24 hours. This method is simple and inexpensive, but has the following disadvantages.

a. The results of the study are influenced by the direction and speed of the wind, air humidity and precipitation.

b. A small amount of particles settles in 24 hours.

in. Coarse particles are deposited on the glass.

2. Volumetric methods are based on the fact that particles suspended in air are delayed by an obstacle installed in the air flow path.

a. Rotary sampler. A collecting surface coated with a special substance rotates for a certain time at a given speed. The result of the sample is expressed as the number of particles settled on 1 cm2 in 24 hours. This method eliminates the influence of wind speed and direction on the results of the study. In the Rotorod sampler (Sampling Technologies Inc., Figure 3.2), the collecting surface is acrylic rods coated with a thin layer of silicone grease. In other devices, the collecting surface does not rotate constantly, but periodically, which avoids its overflow, in the intervals between rotations it is covered with shutters. The American Academy of Allergology and Immunology recommends using these instruments as standard volumetric sample intakes.

b. Aspiration samplers pass air through membrane filters with a known pore diameter, so particles of a given size settle on the collecting surface. Burchard's spore trap is based on this principle (see Fig. 3.3), the collecting surface of which moves at a speed of 2 mm / h, which makes it possible to monitor the change in the concentration of particles in the air throughout the entire observation period. Since the instrument has a weather vane, the direction of the wind does not affect the results of the samples. The more sophisticated AccuVol probe (see Figure 3.4) picks up particles smaller than 1 micron in diameter.

3. Evaluation of the results

a. Using gravitational methods, only large particles (more than 20 microns in diameter), such as ragweed pollen, can be detected in air samples. For scientific purposes, more accurate volumetric methods are used. Guides exist for determining spores of fungi and pollen. Tables compiled from quantitative microscopic studies of air samples allow us to determine seasonal peaks in pollen concentration and fungal spores in different states at one time or another (see Appendix VI). There is no clear connection between the exacerbation of atopic disease and the average daily concentration of allergens in the air, as determined by quantitative microscopic examination. This is because with a low average daily concentration of allergens, exacerbation of atopic disease can be triggered by a short-term increase in their concentration. In addition, quantitative microscopic examination does not always allow an accurate determination of the concentration of airborne allergens.

b. Labeled antibodies are used to quantify allergens using immunological methods. A connection was established between the concentration of allergens determined by immunological methods and exacerbation of atopic disease, especially exogenous bronchial asthma. However, there are few such studies, only data on the ragweed antigen E, allergens of insects and fungi of the genus Alternaria have been published. Immunological methods for studying airborne allergens that are not microscopically detectable, such as particles of the epidermis of animals and insects, are very accurate. In some cases, these studies can establish the cause of allergies.

B. Allergens of pollen. Pollen consists of many pollen grains containing male gametes and used for sexual reproduction of seed plants. In entomophilous (pollinated by insects) plants with bright and fragrant flowers, pollen is large, sticky, spreads, as a rule, over small distances, its concentration in the air is low. In anemophilic (wind-pollinated) plants, the flowers are small, invisible, odorless, and pollen is small, non-sticky, with a smooth and even surface. The cause of an allergy is usually the pollen of anemophilous plants, because its concentration in the air during flowering is much higher than the pollen concentration of entomophilous plants. Pollen is released in most anemophilous plants in the early morning, but its concentration in the air usually becomes the maximum day or early evening. This is due to the fact that air circulation increases during the day. In dry weather, even under the influence of a weak wind, pollen can spread over long distances, so even in large cities the concentration of pollen in the air can be very high. Although pollen loses viability after a few hours, its allergenic properties persist for a long time. Appendix VI contains a floristic map of the USA and Canada and a list of flowering plants common in different floristic regions.

1. Ambrosia. The main cause of allergic rhinoconjunctivitis in the United States is ragweed pollen (Ambrosia spp.), A member of the Asteraceae family. In the northeastern United States and the Mississippi River Basin, ragweed is especially widespread because the fertile, cultivated soil in these areas is ideal for its growth. There are two pollen ragweed antigens - antigen E (Amb aI) and antigen K (Amb aII). Both are well studied. Antigen E is a polypeptide with a molecular weight of 37,800, antigen K is a polypeptide with a molecular weight of 38,000. Antigen E is only 6% of the protein fraction of pollen extract, but it is 200 times more active than antigen K.

2. Cereals. It is difficult to distinguish cereal pollen by morphological characteristics, therefore, when it is detected in air samples, it is first of all taken into account which cereals are common in a given area.

a. In the southern regions of the USA and on the southern coast of the Pacific Ocean it is widely distributed by porcupine, in the northeast and in the northern part of the Mississippi River basin - bluegrass, timothy grass, team hedgehog, and white field polehorse (see Appendix VI).

b. An allergy to pollen of herbs, including cereals, develops only during their flowering period, which depends on climatic conditions, therefore, each region has its own seasonal peaks of incidence. So, in the northern regions, the peak incidence occurs in spring and summer, in the southern regions the frequency of exacerbations during the year almost does not change. At high altitudes, for example, in the Rocky Mountains, and in the northern US states (Wisconsin, Michigan, Maine), pollen concentration is low.

in. In the United States, cereal pollen ranks second after ragweed pollen in frequency and severity of allergic reactions caused by it. In other countries, it is the most significant air allergen.

d. Bluegrass pollen, timothy grass, white field and hedgehogs of the national team have similar antigens and cause cross-allergic reactions. The pollen of pigs is significantly different in antigenic composition from the pollen of other herbs and does not cause cross-reactions.

3. Trees. Allergy is usually caused by pollen from anemophilous trees. The pollen of entomophilous trees, for example fruit and ornamental trees, causes allergies extremely rarely. Do not cause allergies and pollen of anemophilous trees, covered with a dense outer shell.

a. The pollen of different trees has clear morphological features. In addition, trees vary in duration, intensity and flowering season.

b. Since the pollen of trees of different genera has very few cross antigens and trees of a certain genus usually prevail within one floristic region, it is allergic to pollen of trees of only one genus.

in. Since the flowering period of trees is usually short, exacerbation of allergies to their pollen is also short-lived.

The flowering of deciduous trees begins before, during, or shortly after the appearance of leaves. In temperate regions, the flowering season ends in late spring, when the trees are completely leafed. In warmer areas, the flowering season lasts longer (see annex VI).

G. Allergens of fungi. Mushrooms are widespread and live in almost all climatic regions. Mushrooms can be found in soil, fresh and salt water. By type of nutrition, mushrooms are divided into saprophytes and parasites.

1. The structure of mushrooms. According to morphological characteristics, all fungi are divided into yeast and mycelial. Yeast fungi consist of individual cells that reproduce asexually - by division or budding. Mycelial fungi belong to multicellular organisms and represent a network of branching filaments - hyphae that can form spores. Mushroom spores are carried by water, wind and animals. Mold is the reproductive organs of different types of fungi located on the surface of the nutrient substrate. The mold consists of intertwined hyphae and spores and is an amorphous mass, which can have a different color, shape and texture.
Mold fungi are not a taxonomic, but the traditional name for mold-forming mushrooms.

2. The classification of fungi is based on the method of reproduction. Fungi multiply by fragmentation of hyphae and spores that are formed asexually (simple cell division) and sexually (fusion of two cells to form a zygote). In the life cycle of most fungi, the stages of asexual — the imperfect stage — and the sexual — perfect — stage of reproduction alternate. According to the modern classification, mushrooms are divided into 4 classes: Ascomycetes, Basidiomycetes, Zygomycetes and Oomycetes. Mushrooms of the genera Alternaria, Penicillium, and Aspergillus previously belonged to the class Deuteromycetes (imperfect fungi that reproduce only asexually), and according to the modern classification, they belong to the subclass Hyphomycetes of the class Ascomycetes (see Table 3.1). It is these mushrooms that most often cause allergies. Since the classification of Hyphomycetes is based only on the morphology of spores and does not reflect other characters, different fungi included in this subclass significantly differ from each other in antigenic composition.

3. The prevalence of mushrooms. Due to the huge variety and exceptional ability to survive in different climatic conditions, mushrooms are ubiquitous. They remain viable even at low temperatures. They are few in arid and highland areas where there is insufficient moisture and oxygen. House mushrooms often cause year-round allergic diseases. There are a lot of mushrooms in the living quarters in the old furniture upholstery, room humidifiers, shower curtains, plumbing, in trash cans, food waste, raw cellars.

4. Contact with mushrooms. Allergic diseases caused by fungi occur with periodic exacerbations caused by an increase in the concentration of fungi in the air, for example, after visiting a forest or farm, harvesting hay or grain, collecting fallen leaves, in a moist, warm summer and autumn after leaf fall (see Table 3.1). Representatives of some professions - growers, gardeners, workers of paper mills - are especially often in contact with mushrooms. The so-called New Year aggravation of an allergy to mushrooms is due to the fact that there are a lot of them on spruce trees, and the sharp smell of needles and dust from Christmas decorations contribute to the exacerbation of the disease. Methods of controlling fungi are described in Sec. 4, p. III.D.

5. Laboratory research. The best way to prevent allergies to fungi is to constantly monitor and control their content in the environment. Laboratory studies are necessary to: 1) determine the fungi that caused the allergic disease, for example, exogenous allergic alveolitis, 2) evaluate the effectiveness of the control of fungi, 3) determine the types of fungi that are common in the area.

The quantitative determination of fungi present in the air is based on microscopic examination of samples obtained using volumetric methods and cultures obtained by sowing these samples. For the cultivation of mushrooms, Saburo medium and agar with potato starch or corn flour are usually used. The definition of mushrooms requires time, special equipment and professional skills. It should be borne in mind that certain cultivation conditions, such as temperature, air humidity, atmospheric pressure, favor the growth of fungi that do not have clinical significance. Mold fungi, which are especially often allergic, are listed in the table. 3.1 and annex VI.

D. Epidermal allergens. Most often, allergies are caused by the epidermis of dogs and cats, as well as wool (most often goat or sheep) and a feather (for example, duck) used for stuffing furniture, pillows and feather-beds. Treated wool and skins are less likely to cause allergies, since the most powerful allergens are water soluble and are removed during processing. Many epidermal allergens are also found in animal saliva and urine. Epidermal allergens are very active, and even short contact with them can cause a strong allergic reaction. The most active epidermal allergens include feline epidermis antigens. Particles of the epidermis of cats are very small (less than 2.5 microns), slowly settle and accumulate in the air, so even a short stay in the room where the cat lives can provoke a violent allergic reaction. Since these are epidermal allergens, both long-haired, short-haired and non-shedding animals cause allergies. In homes and apartments, the spread of epidermal allergens is facilitated by central air heating systems. Cleaning and washing animals are temporary and ineffective anti-allergic measures. Epidermal allergens can cause occupational allergic diseases. People who live in apartment buildings and in poor condition often have allergic reactions to the epidermis and urine of rodents.

E. Other airborne allergens

1. Household dust consists of mushrooms, plant fibers, food particles, scales and insect excrement, particles of the epidermis of animals and humans. Concentration of house dust is especially high in unventilated rooms.

2. Microcites. It has long been known that dust accumulating in mattresses is a powerful allergen. In 1967, European researchers found that the mites of Dermatophagoides pteronyssinus living in this dust have allergenic properties. In North America, mites of Dermatophagoides farinae are more common. Mites live on particles of the epidermis of humans and animals and accumulate in upholstered furniture, pillows and carpets. The number of mites increases in September and October. Погибшие микроклещи сохраняют антигенные свойства. У вида Dermatophagoides pteronyssinus выделены антигены Der P1 и Der P2, а у вида Dermatophagoides farinae — антигены Der F1 и Der F2. В максимальных концентрациях эти антигены обнаруживаются в экскрементах микроклещей, поэтому для профилактики аллергии следует не только уничтожать насекомых, но и полностью их удалять. Частицы пыли, содержащие микроклещей, довольно крупные и быстро оседают, поэтому аллергические реакции на них возникают не так быстро, как на эпидермис кошек, и обычно бывают менее выраженными. Попаданию в воздух большого количества микроклещей способствует чистка ковров, мягкой мебели, постельных принадлежностей.

3. Семена. Хлопчатник, лен и капок широко используются при производстве волокна. Изделия из этих волокон почти не содержат аллергенов, однако неочищенное сырье, традиционно применяемое в качестве набивки, содержит семена и части цветков, которые являются сильными аллергенами. В связи с этим перед проведением внутрикожных проб с экстрактами семян этих растений следует обязательно проводить пунктационные пробы или определять уровень специфических IgE в сыворотке.

4. Фиалковым корнем в парфюмерии принято называть луковицы растений семейства касатиковых. Поскольку порошок из них обладает аллергенными свойствами, он используется лишь в производстве дешевой косметики и парфюмерии.

5. Аллергенными свойствами обладает порошок из высушенных цветков некоторых видов растений рода Pyrethrum, применяемый в качестве инсектицида.

6. Камеди карайи, акации и трагаканта, входящие в состав жидкостей для завивки волос, также изредка вызывают аллергию.

7. Частицы насекомых. У больных с аллергией часто бывают положительными кожные пробы с аллергенами насекомых. Это свидетельствует о том, что причиной аллергических заболеваний может быть контакт с частицами насекомых. У больных с атопическими заболеваниями, живущих в перенаселенных и плохо убираемых домах или работающих на продуктовых и других складах, аллергию часто вызывают тараканы. Предполагается, что вдыханием частиц насекомых могут быть обусловлены обострения атопических заболеваний дыхательных путей. Описаны вспышки бронхиальной астмы в период вылета ручейников, моли, поденок, бабочек и мошки. Определить насекомое, послужившее причиной массового обострения бронхиальной астмы, до последнего времени не удавалось, поскольку даже под микроскопом не удается определить видовую принадлежность частиц насекомых. Возможно, современные иммунологические методы исследования позволят изучить роль разных насекомых в развитии аллергических заболеваний.

II. Неблагоприятные факторы окружающей среды

А. Климатические условия. К неблагоприятным климатическим условиям относятся высокая влажность воздуха, резкие перепады температуры и атмосферного давления. Несмотря на то что чувствительность к этим факторам индивидуальна, неблагоприятные климатические условия в целом отрицательно влияют на течение аллергических заболеваний, особенно бронхиальной астмы.

Б. Загрязнение воздуха

1. Смог образуется при сгорании жидкого и твердого природного топлива. Степень загрязнения воздуха промышленным смогом оценивают по содержанию окиси углерода, взвешенных частиц и двуокиси серы. При сильном загрязнении воздуха учащаются приступы бронхиальной астмы. Это обусловлено совместным действием всех компонентов промышленного смога.

a. Окись углерода даже в максимальной концентрации (около 120 мг/м3), регистрируемой в городе в часы пик, не ухудшает показатели функции внешнего дыхания как у здоровых, так и у больных бронхиальной астмой.

b. Твердые частицы, например пыль, дым, сажа, при вдыхании могут вызвать кашель и бронхоспазм. В присутствии твердых частиц усиливается неблагоприятное действие на органы дыхания других веществ, загрязняющих воздух.

in. Уровень двуокиси серы в атмосферном воздухе обычно не превышает 1,95 мг/м3. Экспериментально установлено, что вдыхание воздуха с высокой концентрацией двуокиси серы (22—65 мг/м3) вызывает бронхоспазм и снижение активности мерцательного эпителия бронхов.

2. Фотохимический смог состоит из озона (его содержание в фотохимическом смоге обычно превышает 90%), двуокиси азота и других окислителей и образуется под действием ультрафиолетового излучения из углеводородов, содержащихся в выхлопных газах. В низкой концентрации фотохимический смог оказывает раздражающее действие на слизистые глаз и дыхательных путей, в высокой концентрации — приводит к снижению ЖЕЛ, ОФВ1 и нарушению газообмена. Двуокись азота оказывает прямое токсическое действие на легкие, а у курильщиков может привести к необратимым изменениям в легких.

В. Загрязнение воздуха в помещениях. В зданиях с закрытыми вентиляционными системами приток внешнего воздуха отсутствует, что приводит к повышению концентрации в воздухе загрязняющих веществ — дыма от угольных и газовых обогревателей систем центрального воздушного отопления, каминов, бытовых керосиновых и электрообогревателей, а также паров растворителей, например формальдегида, входящего в состав клея для напольных покрытий. Пассивно вдыхаемый табачный дым вызывает гораздо более выраженные, чем предполагалось раньше, нарушения дыхания, особенно у детей младшего возраста. Дополнительную информацию о загрязнении воздуха в помещениях можно найти в литературе, приведенной в конце главы.

Г. Вирусы и бактерии. Доказательств того, что вирусы и бактерии могут вызывать аллергические реакции, нет. Однако хорошо известно, что они способствуют развитию аллергических заболеваний и осложняют их течение. Так, синусит может спровоцировать бронхиальную астму и в то же время стать ее осложнением.
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Воздушные аллергены и неблагоприятные факторы окружающей среды

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