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Allergy Muhammad Hamza Amin Roll 63 Allergy The unusual

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Allergy Muhammad Hamza Amin Roll 63 Allergy The unusual Powered By Docstoc
					                         Muhammad Hamza Amin                                    Roll # 63


Allergy

         The unusual response to a substance that is harmless to others is called Allergy and the substance which
causes this is called Allergen and the person who suffered fro m allergy is called Allergenic.

                   (The inherited tendency of an individual to develop allergy is called “Atopy” )

History of Allergy

                    The concept of "allergy" was originally introduced in 1906 by the Viennese pediatrician Clemens
von Pirquet, after he noted that some of h is patients were hypersensitive to normally innocuous entities such as dust,
pollen, or certain foods. Pirquet called this phenomenon "allergy" fro m the Ancient Greek words allos meaning
"other" and ergon meaning "work". Historically, all forms of hypersensitivity were classified as alle rgies, and all
were thought to be caused by an improper act ivation of the immune system. Later, it became clear that several
different disease mechanisms were imp licated, with the common link to a d isordered activation of the immune
system. In 1963, a new classification scheme was designed by Philip Gell and Robin Coo mbs that described four
types of hypersensitivity reactions, known as Type I to Type IV hypersensitivity. With this new classification, the
word "allergy" was restricted to type I hypersensitivities (also called immed iate hypersensitivity), which are
characterized as rap idly developing reactions.

         A major b reakthrough in understanding the mechanisms of allergy was the discovery of the antibody class
labeled immunoglobulin E (Ig E) - Kimishige Ishizaka and co-workers were the first to isolate and describe Ig E in
the 1960s.

Mechanism of allergy:

        Antibody Mediated Allergy
         1.   The first step is the phagocytosis of allergen by macrophage.
         2.   Then the macrophage exposes outside a part of allergen and a protein MHC(Major Histcompatib ilty
              Co mplex)
         3.   T-ly mphocytes become bound to the allergen and MHC.
         4.   T cells now activate B-ly mphocytes which changes into plasma cells and memo ry B cells (Memo ry
              cells produce antibodies on next attack)
         5.   Plas ma cells produce antibodies (IgE, IgG, IgM )
         6.   Antibodies start to destroy the allergen.
         7.   Allergen-antibody reaction causes the release of histamine and related compounds from certain t issues
              or organs which cause the symptoms of allergy.

                            Example: The example of antibody mediated allergy is Asthma.

        Cell Mediated Allergy
              1.   The first step is the phagocytosis of allergen by macrophages.
              2.   Then the macrophages expose outside a part of allergen and a protein MHC(Major
                   Histcompatib ilty Co mplex)
              3.   T-ly mphocytes become bound to the allergen and MHC.
              4.   T-cells change into killer cell and memory cells.
              5.   Killer cells start to release cytokines e.g. cytotoxins that start to destroy the allergen.
              6.   Cytokines causes the symptoms of allergy.

                            Example: The example of cell mediated allergy is Contact Dermatitis.

Symptoms of Allergy

        Sneezing
        Itching
        Rashes
        Redness of skin
        Eczema
        Watery eyes
        Diarrhea
        Vo mit ing / Nausea

Causes of Allergy

        Foods
        Non-food proteins
        Toxins interacting with proteins
         Genetic basis
        Hygiene hypothesis
        Other environ mental factors
        Acute response
        Late-phase response
        Protein structure and organization
        Protein function
        Proteins and the immune sys tem

Types of Allergens

              1.   Inhalant Allergens
              2.   Ingestant Allergens
              3.   Injectant Allergens
              4.   Contactant Allergens
              5.   Infectant Allergens
              6.   Infestant Allergens

Inhalant Allergens

        These substances produce allergy when they are inhaled. Co mmon examp le is Hay Fever manifested by
sneezing, lacrimat ion, itching and swelling of nose and eyes.

Ingestant Allergens

          These substances produce allergy when they are ingested. General food allergy symptoms are GIT
disturbance, Skin rash; Puffed lips and nose, etc. milk allergy, coffee allergy, cod liver oil and orange ju ice oil
allergy are under this category.
Injectant Allergens

         These substances produce allergy when they are injected. Penicillin (present in 1-5/10,000 population),
liver and glandular ext racts ands insects are Injectant allergens.

Contactant Allergens

          These substances produce allergy when they are contacted to skin. Cos metics, poison plants and drug like
antibiotic solutions are Contactant Allergens.

Infectant Allergens

        Living organis ms like bacteria, mo lds and protozoan may cause allergy by releasing their metabolic wastes
in human body e.g. bronchiectasis.

Infestant Allergens

         Parasites like hookwo rm, tapeworm, roundworm, p in worm and thread worm may cause allergy by
releasing their metabolites wastes and growth products in human body.

Diagnosis of Allergy:

         Diagnosis of allergy is based on the knowledge of 2 things:

    1.   Et iology of allergy
    2.   Identificat ion of allergy

Physical Diagnosis

         It is based on the physical examination of sympto ms of allergy. This method is not exact for the diagnosis
e.g. asthma can be intrinsic or ext rinsic. First is pathologic and second is allergy.

Chemical Laboratory Tests

         These tests are used to identify allergy. In these tests serum IgE level is measure fro m which allergy and its
source is diagnosed.

    1. Blood testing

          Various blood allergy testing methods are also available fo r detecting allergy to specific substances. This
kind of testing measures a "total IgE level" - an estimate of Ig E contained with in the patient's serum. This can be
determined through the use of radiometric and colormet ric immunoassays.

    2. Sensitivity test

Observations of these tests are:

        Negative           No reaction
        Doubtful           No reaction apart fro m slight erythema
        One plus           Erythema of diameter less than 20 mm
        Two plus           Erythema of diameter more than 20 mm
        Three plus         wheal with erythema
        Four plus          wheal with pseudo pods and erythema




Skin Endpoint Titration (SET)

          Also called an intra dermal test, this skin end point titration (SET) uses intradermal injection of allergens at
increasing concentrations to measure allerg ic response. To prevent a severe allerg ic react ion, the test is started with a
very dilute solution. After 10 minutes, the injection site is measured to look for gro wth of wheal, a small swelling of
the skin. Two millimeters of growth in 10 minutes is considered positive. If 2 mm o f growth is noted, then a second
injection at a h igher concentration is given to confirm the response. The end point is the concentration of antigen
that causes an increase in the size of the wheal followed by confirmatory whealing. If the wheal gro ws larger than
13 mm, then no further in jection are g iven since this is considered a major reaction.

Prick Test

          This test measures specific Ig E attached to cells in the skin important in allergies called " mast" cells. Skin
prick testing is usually the first test recommended when an allergy is suspected. The advantages are that it is a
simp le, quick (providing results within 15-20 minutes) and inexpensive form of testing.

          It can give useful information in all forms of allergy, and is appropriate for inhaled and ingested (eaten)
allergies. Skin is pricked and a drop of allergen solution is added and observations are made after 15-30 minutes. If
the skin develops a red, raised itchy area (called a wheal); it usually means that the person is allergic to that allergen.
This is called a positive reaction.

Challenge Test

         Challenge testing is when small amounts of a suspected allergen are introduced to the body orally, through
inhalation, or other routes. Except for testing food and medication allerg ies, challenges are rarely performed. When
this type of testing is chosen, it must be closely supervised by an allergist.

Patch testing

         Patch testing is used to help ascertain the cause of skin contact allergy, or contact dermatitis. Adhesive
patches, usually treated with a number of different common ly allerg ic chemicals or skin sensitizers, are applied to
the back. The skin is then examined for possible local reactions at least twice, usually at 48 hours after application of
the patch, and again two or three days later.

Unreliable Test

       There are other types of allergy testing methods that the American Academy of A llergy, Asthma, and
Immunology considers to be unacceptable.

These unreliable alle rgy testing methods are:

        Applied kinesiology (allergy testing through muscle relaxat ion)
        Cytotoxicity testing
        Urine autoinjection
        Skin titrat ion (Rin kel method)
        Provocative and neutralizat ion (subcutaneous) testing or sublingual provocation

Treatment of Allergy

Environmental Control

         Allergy can be avoided by avoiding exposure to the allergen. It is difficu lt to control the environment in the
case of pollen or dust allergy, however masks can be used. In the case of food allergy, this method can easily be
used.

Symptomatic Drug Therapy

         Certain drugs are very effective in suppressing the allergic reactions e.g.

        Antihistamines in Rhinit is and Sinusitis
        Sympathomimet ics in Extrinsic Asthma
        Corticosteroids as Immunosuppressant

Immune Therapy

          It is also called desensitizat ion. It involves the administration of gradually increasing amount of allergen to
a subject until it reaches the tolerant level. It may take three months to five years. Tolerance is developed due to the
production of IgG blocking antibodies which destroy allergen before it meets Ig E. The mechanism also decreases
the cell responses. The most common techniques of Immune Therapy are:

        Pre-seasonal Therapy (3-6 months before the allerg ic season)
        Co-Seasonal Therapy (during the allerg ic season)
        Perennial Therapy (through out the year)

Common Allergies

The common allergies are

        Peanut allergy
        Pollen allergy(seasonal Hay Fever)
        Latex Allergy
        Lactose\ Milk allergy
        Coffee allergy
        Animal A llergy

Peanut allergy

    Peanut causes allergy. Exposure to peanut can occur in three ways:

        Direct contact

         The most common cause of Peanut allergy is eating peanuts or peanut containing foods. Sometimes direct
    skin contact with peanut can trigger an allergic reaction.
   Cross Contact

            This is the unintended introduction of peanuts into a product. This is generally resulting of the
    exposure of peanut during processing or handling of food product.

   Inhalation

            An allerg ic react ion return may be occurred if someone inhaled dust or aerosols containing peanut.
    Such as peanut oil through the spray.

Pollen Allergy (Seasonal Hay Fever)

     Pollen cause allergy. Pollen grains contain a chemical that binds to the antibodies (IgE). This antibody is
bound to mast to Mast Cells in the mucous membrane of the eye, throat, lungs and nose. This stimu lates the
body to produce histamine and other mediators that cause swallowing in the body. The first exposure to the
pollen leads to a sensitizat ion and the next exposure to pollen causes the allerg ic react ions.

Latex Allergy

    Latex causes allergy. Heva Brasiliensis contains HBPA allergen that is water soluble protein and
causes Type-1 Hypersensitivity reaction.



                    Muhammad Hamza Amin                                     Roll # 63

				
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