Biology Notes on Allergens | Microbiology

The below mentioned article provides notes on allergens.

In 1906, Anton Van Pirquet introduced the term allergy to denote any altered capacity of body to react with a foreign substance. Now it is established that these phenomena are mediated by immune responses of the body. However, if an immunological cause damages the body cells, it is called hypersensitivity. Now-a-days, the two terms allergy and hypersensitivity are used synonymously.

Allergy is caused by certain biological and abiological agents present in the atmosphere. The allergy causing agents present in air are called aeroallergens, and the allergy caused by them is called aeroallergy. Some of the prominent aeroallergens are house dusts, pollen grains, cosmetics, microbial spores or cells, etc. (Table 32.2).

There are four major types of allergic reactions viz., Type I, IgE-dependent, Type-II, cytotoxic tissue specific antibody, Type-III, toxic antigen-antibody complexes with activated complement, and Type-IV, T-lymphocyte cell- mediated hypersensitivity.

The role of Type-I allergy is very common in vast majority followed by Type-III allergy:

Recently, the World Health Organisation, Interna­tional Union of Immunological Societies of Allergy No­menclature sub-committee has revised the names of al­lergens. Instead of italicising the names, the new names are written by using the first three letters of the genus and the first letter of the species and a number. For example, the mite allergens for Dermatophagoides pteronyssinus are written as Der P₁, Der P₂ and so on.

Some allergens have been discussed below:

1. House Dust Allergens:

Generally, house dust is a mixture of hairs, moulds, bacteria, decomposed parts of cloths or furniture, small insects, mites, etc. These are inhaled by individuals who later on suffer from allergy.

The most common fungal spores isolated from the allergic individuals are the species of Aspergillus, Rhizopus, Cladosporium, Curvularia, Helminthosporium, Phoma, Fusarium, Cephalosporium, Nigrospora, Cladosporium, Epicoccum, Penicillium, etc. A significant work on respiratory allergy has been done at V.P. Chest Institute (Delhi), and at the other centres viz., Jaipur, Kanpur, Lucknow, Kolkata and Aurangabad.

Mites are the important components of house dust and strong allergens for humans. Some mite species are Dermatophagoides farinae, D. gallinae (poultry mite), D. domesticus, D. destructor, D. pteronyssinus, etc. Among these D.pteronyssinus has been most extensively studied. D. pteronyssinus is found in large number on mattresses, blankets, pillows; etc where human scales are abundant. These are distributed in all houses equally.

D. pteronyssinus is commonly known as house dust mite which dominate by 88% almost in all houses. Children shed considerable amount of skin in house, which serves as a culture medium to D. pteronyssinus.

Thus, human skin is a good source of nutrients in the house dust. A significant work on allergenic parts of mites has been done. Cunnington (1972) found that the dead mites and their different body parts, faeces and secretions are equally potent allergens as the live mites.

The housewives, domestic cleaners, upholsterers and decorators are found to be victimised by house dust mite. Torey (1981) also reported that mite faeces are the major source of house dust allergens. They are related to the presence of mites, and radioimmunoassay revealed more than 95% of the allergen accumulating in mite cultures was associated with faecal particles.

2. Pollen Grains:

The climatic conditions in India vary in different regions; therefore, variations also occur in vegetation. Due to great diversity in vegetation and climatic conditions the aeroallergens are also of different types in different regions and places.

In India aero allergenic pollen grains are contributed mainly from the plants belonging to the family Poaceae, Chenopodiaceae, Amaranthaceae and Asteraceae. Tilak and Vishwe (1979) recorded 33 pollen types of which herb pollen grains were the highest in number. After attaining maturity, the pollen grains get disseminated and dispersed through vectors like wind, water and insects.

Occurrence and abundance of pollen grains in the environment differ according to season and vegetation types. However, most of the pollen grains are found throughout the year.

Allergenic potential of pollen grains is governed by their chemical constituents. Chakraborty (1998) have analysed and clinically tested the allergenic potential of some common pollen grains recorded in Kolkata viz., Areca catechu, Azadirachta indica, Carica papaya, Catharanthus, Phoenix and Datura.

They reported 49% sensitivity by Azadirachta pollen grains followed by Datura (35%) and Catharanthus (26%). Chemical nature of these pollen grains showed differences in total carbohydrate, total protein and total lipid composition.