By Nermina Lamadema,
Postdoctoral Research Associate at King's College London
Human immune system sometimes responds inappropriately to harmless substances such as pollen, various foods or a house dust mite with a range of symptoms that come under the common umbrella of the term allergy. These substances termed allergens normally do not cause reaction in people but can trigger an immune system response in people with allergies who can sometimes be very severe. Allergy is a systemic disorder which belongs to the group of autoimmune diseases where an immune system mounts an attack against itself causing the destruction of its own tissues.
What is the Cause of Allergies?
There are several key factors which are believed to be the greatest contributors to the raise in the incidence of allergies. The chances of developing an allergy increase in children that are born in families where allergies already exist which points to the role for genetics particularly as the likelihood of a child becoming allergic doubles if the mother has an allergy and if both parents are allergic the overall risk increases to 80%.
Second important factor contributing to the raise in allergies belongs to the diet and lifestyle particularly in the light of the fact that we have become increasingly reliant on processed, nutrients and vitamin poor foods.
The lifestyle which is sedentary and lacking in exercise with more time spent indoors rather than in natural sunlight, has led to the epidemics of Vitamin D deficiency. The early development of the immune system depends on the availability of Vitamin D and there is a demonstrated link between Vitamin D deficiency and allergy.
Finally, the environment we are exposed to particularly in the early life plays important role in allergy development. In this context it is worth mentioning The Hygiene Hypothesis. This hypothesis proposes that early immune system development in individuals can only work effectively if there is an exposure at a very early stage of infancy to a certain amount of bacteria and microorganisms in everyday environment. Today’s environment is very different to around a hundred years ago and is characterised by an increase in preoccupation with cleanliness becoming progressively more sterile. Cleaning reagents used routinely in households contain anti-microbial agents and the food preparations have become overtly hygienic. In today’s industrialised world people tend to live in cities whereas in the past many children used to be exposed to farm life and living with animals. Helminth parasitic infections where a common occurrence in childhood in the past and they are responsible for the development of a specific type of immunity which appears to provide allergy protection. Helminthic parasitic infection nowadays affect around a third of world population predominantly in developing countries. These infections typically occur in childhood and exert the lifelong effect on the host immune system. There is an inverse relationship between the helminth infection and the autoimmune diseases spread worldwide. More developed western countries with fewer helminthic infections show greater increase in the number of immune system disorders.
Types of Allergens
There are many types of allergens such as Foods (nuts, milk, fish, wheat and eggs), Pollen, Dust mites (microorganisms found in bedding, carpets and clothing), Moulds (fungi such as black mould found on windowsills and on decaying food), Animals (domestic pets or more specifically saliva, sweat and urine which ends up on their hair and skin cells-dander) and Insect stings and bites (wasp’s bees and hornets, mosquitoes, bedbugs, mites, flies, fleas, midges and ticks). Their allergen is venom injected into the skin of the person as the result of a sting.
Symptoms of allergies
Most common symptoms of allergic reactions involve minor localised skin irritations, such as itching, redness, hives, rhinitis, runny nose, watery eyes and wheals. However, in some cases allergic reaction can be very severe resulting in anaphylactic shock which can be life threatening if untreated. Anaphylaxis is an extreme allergic reaction which occurs rapidly and affects the whole body characterized by severe facial itching resulting in a red rash and swelling particularly in the region of the mouth, throat and tongue leading to breathing and swallowing difficulties.
The Allergic Cascade
The Allergic Cascade is a three step event involving mast cells or mastocytes which are a type of blood cell which releases chemical granules called histamine.
First stage is Allergen Sensitization which isthe initial allergen exposure either via inhalation or ingestion. Second stage is Early-phase allergen response involving the mast cells – specialized cells with surface IgE receptors which are the sites of IgE antibody binding. Two adjacent mast-cells are sensed by an allergen which attaches itself to both and the two IgEs become cross linked leading to histamine release. Histamine is a chemical which increases blood vessel permeability (vasodilation) allowing the fluid to escape from capillaries into the tissues giving raise to allergic symptoms. Final stage is Late-phase allergen response which only occurs with serious allergic complications.
Immunoglobulin E
Antibodies or Immunoglobulins are Y-shaped glycoproteins produced by specialized white blood cells called B-lymphocytes or the B cells. Antibodies are produced in response to harmful substances which the immune system recognizes as foreign in nature called antigens. Microorganisms such as bacteria and viruses are examples of antigens. Structurally antibody contains two heavy and two light chains with the light chains being responsible for antigen recognition and binding.
Antibody molecule with 2 heavy chains (pink) and two light chains (green)
Antibodies can be grouped into five different isotypes: IgG, IgM, IgA, IgE and IgD Immunoglobulin E (IgE) is the isotype found in small concentrations in the blood of healthy individuals but in allergy sufferers the levels of IgE are significantly increased.
How are the allergies diagnosed?
Typically, Skin prick testing (SPT) can be used to diagnose airborne allergens, foods and insect venom allergies. The procedure involves placing a tiny amount of allergen into the skin on the inner forearm which results in a small localised allergic response in the form of a bump and redness occurring at the site where the allergen had been placed. This way up to 25 allergens can be tested at once.
Alternatively, blood test can be used to determine the total amount of circulating IgE.
Finally, to test the allergic response to the causes of eczema or skin irritations typically patch testing is used.
Current Allergy treatments
Depending on the type of allergy symptoms different approaches can be used such as for example Anti histamines to treat symptoms of an allergic reaction and provide relief but not a cure. Antihistamines function as antagonists of histamine and are available in a number of formulations from tablets to creams for topical use to eye and nasal drops.
Decongestants are usually prescribed with antihistamines to treat the symptoms of nasal congestion. Corticosteroids are used to decrease inflammation and nasal blockage and are available as creams, nasal sprays, pills and asthma inhalers. Epinephrine (Adrenaline) Epipen® is single dose injection which serves as a first line of emergency response in the cases of anaphylaxis. In the case of emergency the patient auto injects into their muscle which activates the device and delivers a dose of adrenaline after 5-10 seconds. It is important that the drug is not delivered into the vein directly because that can be fatal.
All of these treatments only provide a temporary relief for the unpleasant symptoms of allergies, however there is currently no cure for the allergy itself. This means that a lot of research has been put into various types of therapies in an attempt to find a cure.
Članak „Alergije“ na bosanskom jeziku možete pročitati u četrnaestom broju magazina AŠK, septembar 2016.