Introduction
Allergens are substances capable of sensitizing the animal body so that unusual responses occur. According to defined by Medline Plus, allergen is a substance that can cause an allergic reaction. In some people, the immune system recognizes allergens as foreign or dangerous. As a result, the immune system reacts by making a type of antibody called IgE to defend against the allergen. This reaction leads to allergy symptoms On the other hand, allergy means a changed or altered reaction. An allergic individual develops an unusual reaction to a substance which is harmless to others. Almost any substance whether of biological or synthetic origin may prove to be allergenic to hypersensitive persons.
Mode of Action of Allergens
The allergenic material is transmitted by direct skin contact by air borne pollens, smoke and dried plant materials and on the coats of animals. Once a person has been sensitized to particular allergens, subsequent exposure to the materials produces an antigen-antibody reaction which results in the liberation of histamine or histamine – like (H-like) compounds which in turn cause the allergic symptoms.
Manifestation: Allergies are commonly manifested as hay-fever, asthma, cold and dermatitis. Desensitization is possible once the specific cause has been established. Allergenic extracts are available for diagnostic and prophylactic treatments.
Common Allergens
1. Pollens
These are responsible for seasonal hay-fever and chronic asthma, pollen counts of the atmosphere are regularly recorded and published in the developed countries like UK and USA, Grass pollens form the highest proportions of the total which may constitute 62% of the total count in summer (June /July) in London. Pollen counts of 10-50 will produce discomfort in susceptible individuals common grasses involved are: Phleum pratensis (Timothy), Dactylis glomerata (cocksfoot) and perennial rye (Lolium perenne)
2. Spores
A number of common moulds produce spores which cause rhinitis and asthma in sensitive individuals. They are often responsible for this conditions which extend beyond the normal pollen season and up to the beginning of frosts. Molds grow in conditions where organic decay is progressing and peak sporulation occurs during hot, dry conditions when the atmosphere may become heavily contaminated. Spores of clasdosporium herbarium, sporobolomyces roseus and tycopodium are common allergens for asthma attacks in the UK
Rhus Spp (Toxicodendron) family Anacardiceae .e.g. Rhus radicans contains contactant allergens which produce severe dermatitis associated with watery blisters which burst and quickly spread across the skin the allergens are contained in the plant sap and are easily transmitted (on clothing, hands, animal fur and as the result of Bush fires) These compounds are known as Urushiols and they belong to a class of akenyl polyphenols found in the anacardiaceae
3. Miscellaneous
Hair, feathers and house dust are materials of natural origins, synthetic products like detergents, dyes and cosmetics may also act as contact allergens.
Predisposing Factors to Allergic Response
Pre-disposing factors to allergic response are.
- Hereditary tendency
- Dysfunction of the endocrine glands
- Increased excitability of sympathetic and parasympathetic nervous systems
- Absorption of toxic metabolic and catabolic substances
- The patic dysfunction and psychic influences.
Types of Allergens
The types of allergic symptoms are dependent on the shock organ affected by the particular allergens and its path of entry into the body. The listed below are Allergens types with different symptoms they present:
1. Inhalant allergens
Inhalant allergens are substances which are distributed in the atmosphere and contact the nasal and buccal mucosa during respiration, the symptoms are restricted to these areas and manifested by sneezing, lacrimation, itching and swelling of nose and eyes. The condition is known as sinusitis or hay-fever, seasonal hay-fever occurs during certain months of the year and usually associated with the release of pollen grains from certain plants hence the term polinosis is often used. Non seasonal hay-fever or perennial rhinitis may be caused by inhalant other than pollens e.g, mould spores, dust, animal epidermis etc.
2. Ingestants
Ingestants are those which occur in foodstuffs. They are responsible for gastrointestinal symptoms but may give rise to skin rash, puffed lips and tongue, migraine, rhinitis, or other more serious ill effects such as bronchial asthma. The activity of the allergens is not localized, one organ or area of the body but it is transferred to other organs by the blood stream.
Examples in children are those foods considered essential to proper diet and growth like cow’s milk, orange juice and cod-liver oil. Some adults are allergic to pea nuts, mango juice, wallnuts and honey.
3. Injectant Allergens
Are present in solutions intended for parenteral administration. The allergic reactions to penicillin are well known to most of the lay public. Other products include liver extract, antitoxins and the glandular products. The symptoms in each case are similar to those of the antibiotic. Itching of the palms of the hands and soles of the feet, and peeling of the skin. Bees and wasps sting allergies are injectant allergens common in many individuals.
4. Contactant Allergens
Contactant allergens are those that come into direct contact with the epithelium. Poison Ivy (Rhus radicans) and other species; Asparagus, Buckwheat, Buttercups, Catalpa leaves, ginkgo leaves, marigolds are few examples of plant excitants of contact dermatitis.