Natural Allergens

Chapter 32

Natural Allergens

ALLERGENS

• Allergens are inciting agents of allergy, i.e., the substances capable of sensitizing the body in such a way that an unusual response occurs in hypersensitive person. Allergen may be biologic, chemical or of synthetic origin. It is common to speak about the substances, such as pollens, danders, dust, etc., as natural allergens. Although the chemical identity of allergen is unknown, but most known allergens are protein or glycoprotein and do not have much difference from other immunogens except perhaps being somewhat smaller in size (mol wt. 10,000–70,000). Most allergenic substances are mixture in composition. Allergens from related sources often are similar chemically and cross allergenic. A number of low molecular weight chemicals (allergenic haptens) are partial immunogens and induce allergy after combining covalently with a suitable protein carrier, viz. drug allergy.

WHAT IS ALLERGY

• The allergy (hypersensitivity) may be defined as a specific immunologic reaction to an immunogen—a normally harmless substance (allergen). It was first defined in 1906 by von Pirquet who described allergy as changed or altered reaction in the body of an individual, in response to a substance or condition that is harmless to others. Sneezing is always considered to be a symptom of a cold but sometimes it is an allergic reaction to something in the air. According to reports available approximately 30% population suffers from some sort of allergic syndrome. However, few persons develop symptoms that are sufficiently severe to require the services of allergist or physician. The occurrence of allergic disease is determined by the characteristic of the individual as well as those of the allergen and even the condition of exposure. Following are predisposing factors which make the person hypersensitive to allergens:

1. Hereditary tendency to allergic response 
2. Dysfunction of the endocrine glands 
3. Increased excitability of sympathetic and parasympathetic nervous systems 
4. Absorption of metabolic and catabolic substances 
5. Hepatic dysfunction and 
6. Psychic influences

TYPES OF ALLERGENS

• The allergens can be classified on the basis of types of symptoms, which depend on the shock organs affected by the particular allergens and its route of entry into the body:

1. Inhalant allergens 
2. Ingestant allergens 
3. Injectant allergens 
4. Contactant allergens 
5. Infectant allergens

Inhalant Allergens

• Inhalant allergens are airborne substances as chemicals, causing respiratory disease, inflammation in the nose and lungs. Inflammation in the nose is manifested by sneezing, lacrimation, itching and swelling of nose and eyes. The condition is known as sinusitis or hay fever. The Oduor emanating from new-mown hay is often responsible for the fever or stuffiness of the nasal passages. Inflammation of lungs is often expressed as asthma. Air pollution, both indoor and outdoor, plays a significant role in the aggravation of airway disease in the asthmatics and may contribute to the overall increase in asthma morbidity

Symptoms of allergies to airborne substances are:

1. Sneezing often accompanied by a runny or clogged nose
2. Coughing and postnasal drip 
3. Itching eyes, nose and throat 
4. Allergic shiner (dark circles under the eyes caused by increased blood flow near the sinuses)
5. The ‘allergic salute’ (in a child, persistent upward rubbing of the nose that causes mark on the nose)
6. Watering eyes, conjunctivitis (an inflammation of the membrane that lines the eye lids causing red-rimmed, swollen eyes and crusting the eyelids) 

• As soon as the allergens land on mucous membrane, an inside lining of the nose, a chain reaction occurs that leads the mast cells in this tissue to release histamine and other chemicals. These powerful chemical contract certain cells of some small blood vessels in the nose, which allow fluid to escape causing the nasal passage to swell resulting in nasal congestions. The allergens that can cause airborne allergies (inhalant allergens) include pollens, dust, mites, mould spores and animal allergy (epidermis or dander).

Pollen allergens

• Pollens are the tiny, egg-shaped, round, angular, square, rectangular or otherwise shaped male cells (organ) of flowering plants. These microscopic, powdery granules are necessary for plant fertilization. The average pollen particle size is less than the width of an average human hair. Most pollen grains are single entities, but some may be two-compound, three-compound, tetrad, or so forth. They may either have no germinal apertures as such (Acol pate) or have many pores (multicolpate) or range in between (decollate, tricolpate, tetrolate). The surface appearance of outer wall (exine) is characteristic; it may range from smooth (psilate) to spiny (echinate) with various intervening gradations (reticulate granulate, cophate).

These pollens can be further classified into two types:

1. Anemophilous (wind pollinated) 
2. Entomophilous (insect pollinated)

Anemophilous: 

• Anemophilous pollens are usually small 15–45 μ in diameter, light, nonadhesive and relatively smooth and are produced by plain looking plants, e.g., trees (oak, walnut); grasses (bermuda grass and timothy) and weeds (ragweed, plantain).

Entomophilous: 

• Entomophilous pollens are usually larger in size (up to 200 μ in diameter), heavier, adhesive and may be somewhat spiny. Plants are scented, with colored flowers such as clover, hollyhock, honey suckle and rose.

• Most common allergic reactions are produced by Wind pollinated (anemophilous) pollens, because of their light weight and the dry nature; these pollen grains are carried for long distances.

• List of plant or tree producing pollens (allergens): Alfalfa, almond, apple, acacia, barley, blue grass, canary grass, cherry, eucalyptus, gladiolus, hazelnut, juniper, mulberry, mustard, lemon and related species of citrus.

Ingestant Allergens

• Allergens which are present in food stuff and swallowed are termed ingesting (food allergy). A food allergy is an immune system response to a food. Once the immune system decides that a particular food is harmful, it creates specific antibody to it.

• The gastrointestinal symptoms are mainly affected by the food allergens, but they also cause skin rash, puffed lips and tongue, migraine, rhinitis or other symptoms like severe eczema of hand and feet. The effects of food allergens are not localized to one organ or area of the body, but it may transfer to other organs by the blood. Thus, an atopic dermatitis, such as tomato rash, strawberry rash, or that caused by eating oranges, chocolate or shellfish, is developed by patients.

• Some most common food allergens ingested by patients are milk, egg, peanut, tree nut (walnut, cashew nut, etc.), fish, shellfish, soy, wheat, orange juice, cod liver oil or other vitamins containing fish liver oils. In addition to the above-mentioned normal food, there are food additive, which also could be allergic to any individual, viz. mannitol, sorbitol, polysorbates, malt-dextrin's, citrus, bioflavonoids, artificial preservatives, artificial coolers, citrus pectin, talc, soy lecithin, gluten, soy flour, rice flour, alfalfa, potato starch and gum acacia.

• Most satisfactory method of combating food allergens is elimination of the offending substance from the diet. Dairy milk allergy is a specific immunologic antibody– antigen reaction due to a lacto-albumin, because heating and boiling alter this protein. Milk allergy may result in severe dermatitis, recurrent rhinorrhea, bronchitis and asthma. Its antigenicity can be avoided by the use of commercial milk substitutes that are prepared from soya bean isolates.

Injectant Allergens

• Injectant allergens cause symptoms similar to those of the antibiotics, e.g. penicillin, cephalosporin and semisynthetic penicillin, etc. Itching of the palms of the hands and the soles of the feet, erythema and peeling of the skin are characteristic. In severe cases anaphylactic shock may occur. The natural sources of injectable allergens are produced by the sting of bees, hornets and wasps. The allergens injected by the stings of such insects can induce severe local and constitutional reactions sometimes causing death. In addition to penicillin products, other injectable that may cause allergies are liver extract, antitoxins and the glandular products.

Contactant Allergens

• A number of plants and their products have been identified as the causes of contact allergies. The plant most responsible for contact dermatitis in North America belongs to the Ascidiacea family, primarily the genus Toxicodendron (Rhus) and includes poison ivy, oak and sumac. The allergen component of these plants, called urushiol (a phenolic compound) are found in the oleoresin fraction and are derivatives of pentadecylcatechol or heptadecylcatechol. Many plants of Compositae family, which include the ragweeds, also cause contact dermatitis and the allergens responsible had been identified as Sesquiterpenoids lactone.

• Other plants species, which can give rise to contact allergic reactions are Rutta graveolens, asparagus, ornamental ‘dumb cane’ (Dieffenbachia Seguine), buck wheat, butter cups, catalpa leaves, chrysanthemums, ginkgo leaves, lobelia, marigolds, may-apple, Osage orange, flowering spurge, snow on the mountains and smart weeds.

Infectant Allergens

• Allergy caused by the metabolic product of living microorganism in the human body, such as the continual presence of certain types of bacteria, protozoas, Moulds, helminths and other parasites in the body of human being that are responsible for chronic infection for which patients are not aware. Often the metabolic product of their growth causes some patient sensitized and the patient may exhibit allergic symptoms, which does not response positively to routine skin test for inhalant allergens. In such patients, bacterial metabolic wastes are considered to be infectant allergens.

• The continuous presence of growth products and metabolic waste of parasitic organism such as hookworms, tape worms, pinworms, threadworms and dermatophytes are referred as infectant allergens.