An allergy is an immune response to a foreign substance in the body. Substances that initiate an immune response to cause allergy are called allergens. Examples of allergens are Pollen grains, dust, food like egg protein, cuticles of prawns, molds, ticks, carbohydrates like lactose, and some medicines.
Causes
It may depend on the heredity, sex, age, and race of the host.
Environmental factors like allergens, pollution, exposure to infections in early childhood, and diet are also responsible.
How does it happen?
1. When the body comes in contact with an allergen it triggers an antibody response. There are two types of immune response: primary and secondary.
A. Primary immune response - It occurs when the first time the body comes in contact with an antigen. The humoral response, mediated by B cells with the help of T cells, produces high-affinity and antigen-specific antibodies (1). B-cells activated by T cells later move to secondary lymphoid organs like the spleen and lymph nodes where they enter B-cell follicles or germinal centers within the cortex. B cells proliferate inside the germinal centers and undergo changes that affect the affinity of their receptor. They can bind to nerve cells to receive signals from T-cells. B-cells that do not bind to T-cells undergo cell death. B-cells later differentiate into Plasma cells and memory cells.
B. Secondary Immune response- It occurs when the body comes in contact with the same antigen for the second and subsequent times. Vaccination is based on this concept. Once the primary response is triggered, the secondary response occurs when the body encounters the pathogen for the second time due to the memory cells produced in the primary response.
2. Once the antibodies are produced, they bind to mast cells. When this antibody binds to the antigen the mast cells produce histamine. The histamine induces an inflammatory response (redness and swelling).
Symptoms
The histamine released inflames the lining of the nose thus producing excess mucus. This leads to a runny nose, sneezing, sore throat, and watery eyes.
Histamine may lead to the narrowing of lung passages thus causing an asthmatic attack.
Food allergies can affect the bowels and stomach.
Symptoms can be observed on the skin in the form of hives and eczema,
Anaphylactic Shock- Severe allergic reactions to allergens can be life-threatening and need immediate medical attention.
Treatment
1. Antihistamines-Block histamine release from mast cells, e.g. Benadryl (diphenhydramine)
Claritin (loratadine)
Allegra (fexofenadine)
Zyrtec (cetirizine)
Xyzal (levocetirizine)
2. Intranasal corticosteroid sprays (INCS)- Nasal sprays. For example, Beconase.
Beconase AQ.
Flonase.
Nasacort.
Nasalide.
Nasarel.
Nasonex.
Omnaris.
3. Decongestants - Reduces swelling of membranes. Example are pseudoephedrine, phenylephrine, levomethamphetamine, propylhexedrine, synephrine, tetrahydrozoline, naphazoline, oxymetazoline, and xylometazoline.
4. oral corticosteroids- Reduce swelling and avoid severe allergic reactions. Examples are dexamethasone, corticosteroid, hydrocortisone, methylprednisolone, and prednisolone.
5. Adrenaline is given for life-threatening allergic reactions.
6. Non-medicated treatments like saline sprays can be used in sinusitis and rhinitis.
7. Allergen immunotherapy (desensitization) - It is a long-term treatment that changes the immune system's response to allergens. It involves the administration of regular, gradually increasing amounts of allergen extracts, by injections or by sublingual tablets, sprays, or drops.
References
1. Riddell, N.E. (2023). Immune Responses: Primary and Secondary. In eLS, John Wiley & Sons, Ltd (Ed.). https://doi.org/10.1002/9780470015902.a0029196
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