What is Allergy
Abnormal response of Immune system to a paticular substance is said to be Allergy. It is also known as Hypersensitivity. A normal response to an antigen is simply an Immune response, whereas an undesirable response or hypersensitivity to a particular substance or antigen is called Allergy. Autoimmunity, antibodies released against own cells, is also a major allergic immune response.
Causes of Allergy
- Allergens like pollen, dust, fur of animals, mites etc.,
- Certain foods like peanuts, wheat, soy, fish, Milk etc.,
- Insect stings of bees etc.,
- Medications like penicillins, other antibiotics etc.,
- Microbial infections also causes hypersensitivity.
- Seasonal variations may be allergic to sensitive persons.
Types of Allergy and how is it produced
Different types of allergies produced due to food, drugs, seasonal, contact, animal, pollen, microbial spores allergy etc., These immune reactions produced in all the above cases due to Antibody mediated and cell mediated hypersensitivity immune reactions. Coombs and Gell has classified these hypersensitive reactions pathologically into 4 types. These are Type – I,II,III and IV. Type I,II,II have been produced by Antibody mediated response, whereas, IV is a cell mediated immune response.
- Type -I Hypersensitivity : It is an Immediate type of allergy, mediated by IgE (Immunoglobulin -E) antibodies. Also called anaphylactic or Atopic allergy. Mast cells and Basophils have high affinity towards IgE receptors. During Sensitization, histamine and other mediators get released from Mast cells and Basophils. Example – Contact dermatitis, allergic rhinoconjunctivitis
- Type – II Hypersensitivity : It is a cytotoxic type of allergy, mediated by IgM and IgG antibodies. These antibodies bind to the insoluble antigens present on the surface of the own cells. It has two phases. Sensitization phase, where the antigens activates the immune system by producing antibodies. Effector phase involves the activation of Antibodies against the antigens. the destruction of antigens occurs by Antigen-antibody reactions. Example – Autoimmune diseases like Myesthenia gravis, hemolytic anaemia etc,
- Type-III Hypersensitivity : It is an Immune complex reaction activated by compliment system, which activates the antibodies. Antibodies form complex with unbound soluble antigens and fix the compliment of Immune complexes. Example – Arthus reaction(allergy after vaccination), serum sickness, nephritis etc.,
- Type-IV Hypersensitivity : It is a delayed type of reaction mediated by T- lymphocytes. It is a cell mediated Immune response and not antibody mediated response. It takes several days, to act against antigens. Requires a lag time from exposure of antigen to produce activated T- cells onto the antigens. Example – Contact dermatitis, tuberculin skin test, granulomatous inflammation, graft rejections etc.,
Signs and symptoms
- Itchy eyes, conjunctivitis
- Swelling and redness of eyes
- Allergic Rhinitis (hay fever)
- Hives on skin
- Angioedema of soft tissue
- Abdominal discomfort
- Confusion and Tachycardia
- Patient’s history on allergic factors
- Blood tests to detect the release of high WBC count
- Skin tests
- Anti-inflammatory drugs
- Immunosuppressant drugs