Dust mite micro photograph

Relevance of Indoor Allergen Exposure

The prevalence of allergic diseases, including asthma and hay fever (allergic rhinoconjunctivitis), has increased in developed countries around the world during the past decades and continue to increase. According to the American Academy of Allergy Asthma and Immunology, allergic diseases currently affect more than 25% of individuals in the USA. This has impacted the global allergy market.

Many studies suggest that exposure to common indoor allergens is a relevant environmental factor partially responsible for the increase in prevalence of allergic diseases in developed countries. Individuals in these countries spend more than 90% of their time indoors, and therefore exposure to indoor allergens is prolonged. Genetically susceptible individuals exposed to indoor allergens, primarily during infancy, become sensitized to these allergens.

Allergen avoidance can prevent (to some extent) the development of sensitization to allergens and relieve allergic symptoms in allergen-sensitized individuals. Therefore, various medical and public-oriented professional organizations have emphasized the relevance of indoor allergen exposure and recommended several guidelines for affected subjects, encouraging the use of certain measures for optimal indoor allergen avoidance.

Several multi-center studies on asthma and allergens performed at the national level in homes of affected subjects (including the National Cooperative Inner-City Asthma Study and the National Survey of Lead and Allergens in Housing) have demonstrated the usefulness of allergen measurement in monitoring the efficacy of allergen avoidance interventions.

The high prevalence of allergies has contributed to the increased public concern about air quality in homes, schools, and the workplace during the past years. However, due to the growing demand for mold assessments, common allergens (other than fungi) are not typically addressed during the course of indoor air quality inspections, albeit these non-fungal allergens are often the cause of the allergy symptoms experienced by building occupants.

A number of allergens are present indoors. A dose-response relationship between exposure and sensitization has been described for dust mite, cockroach, cat, and dog allergens. Cat and dog allergens are contained in small particles (2-6 um in diameter), which  are passively transported to public buildings. Therefore, cat and dog allergens are ubiquitous and present in the majority of buildings, including those where these animals have never been housed, like new homes and schools, at levels that, in some cases, exceed proposed thresholds to cause sensitization.

Studies performed in several major inner cities of the USA have linked exposure to cockroach, rat, and mouse allergens with asthma, and indicate that these allergens account for 95% of the allergen load present in some homes.

The relevance of indoor allergen exposure during infancy to cause sensitization and development of asthma should be emphasized to the general public. Daycare centers and schools can be critical sites of exposure to indoor allergens, and it has been suggested that these buildings should be target locations for interventions. Epidemiologically, it can be more effective to target one single daycare center or school than multiple homes.

Production of Pollen Extracts: How Pollen Purity is Evaluated

After the pollen used for the production of allergenic extracts has been collected, their identity and purity must be evaluated. Microscopic analysis is performed for this purpose. Currently, pollen purity assessments include counting and identifying biological components contaminating the pollen. However, this method of evaluating pollen purity does not consider either the potential clinical relevance of specific contaminants or their relative volume compared to that of the pollen in the final sample. While the potential clinical relevance of many pollen contaminants is unknown, volumetric counting instead of particle counting could provide a better estimation of the amount of foreign biological materials contained in pollen. However, standardized and approved methods to perform this evaluation are lacking.
For the purpose of microscopic pollen identity and purity evaluations, samples are stained with a solution and examined under various magnifications. Microscopic pollen analysis also can provide valuable information regarding pollen quality for the production of pollen extracts. For example, the presence of a large number of plant parts and a variety of miscellaneous fungal spores generally indicates that the pollen is not sufficiently clean, and that additional activities to remove biological contaminants are necessary. To the contrary, the presence of large amounts of one single spore type, hyphae, and/or sporulating structure indicates that fungi have actively infested the pollen for a period. This pollen should be discarded for the production of pollen extracts.

Qualified individuals should perform the pollen identification and purity assessments in appropriate in-house laboratories at allergen manufacturing companies. However, programs to train individuals and certify such laboratories are currently lacking.
It is essential to perform all activities associated with pollen used for the production of pollen extracts, including identification and purity assessments, in dedicated areas of allergen manufacturing companies where other types of raw materials are not present. Otherwise, cross-contamination of pollen used to produce pollen extracts with other allergenic products will likely occur.

Pollen Collection to Produce Allergen Extracts

Proper pollen collection is essential to produce allergen extracts. Pollen collection is tedious and requires a high level of specialization.
A few large pollen collection entities own land to cultivate the desired plants for pollen collection, under conditions that minimize exposure to man-made pollutants. However, this is an emerging strategy, which often does not allow for the collection of sufficient amount of pollen necessary for the production of pollen allergen extracts. Many small family-owned pollen collection entities also obtain pollen for the production of pollen extracts.

There are three main methods used to collect pollen from wind-pollinated plants; first, the water-set; second, the vacuum; and third, the cut/dry/sieve. Many pollen species can be collected using either method.

The three collection methods have advantages and disadvantages. The main advantage of the water-set method is that it results in very clean pollen. To the contrary, it is very labor intensive and often the resulting pollen is impacted by high moisture and subsequent microbial growth.

The main advantage of the vacuum and the cut/dry/sieve methods is that are relatively simple to perform. Their main caveat is that the resulting pollen often contains high levels of biological contaminants.

Following collection, pollen is dried to reduce moisture content and prevent microbial growth. Subsequently, the naturally present plant parts, fungal spores, insect fragments, and foreign pollen grains are removed. The two primary methods to clean pollen are mechanical gradation sieving and air classification, both described below.
Mechanical gradation sieving is the simplest and most widely used method because such sieving with various micron-sized meshes can remove biologic contaminants. The air classification method can separate particles that differ in both weight and size, resulting in very clean pollen for the production of pollen extracts. Though, air classification machines are expensive and often disrupt pollen, making its quality difficult to assess because some cytoplasmic material containing allergens can be lost during the cleaning process.

Proper understanding regarding pollen collection to produce allergen extracts is essential for allergen manufacturers and clinicians who use pollen allergen extracts.