Allergies are caused by an abnormal response of the immune system to usually harmless substances called allergens. When a person is exposed to an allergen, their body produces antibodies that attach to mast cells and cause them to release chemicals like histamine. Histamine causes allergic symptoms and is involved in allergic and inflammatory processes throughout the body. Allergies can be tested for and treated with medications that reduce symptoms or immunotherapy which desensitizes the immune system to allergens over time.

1. Presented By: Hasnain Sarwar
Roll No. : “4128”

2. What is an Allergy?
• Allergies are caused by an abnormal response of the immune
system. The immune system reacts to a usually harmless substance
in the environment. This substance can be pollen, mold, dust, animal
dander, certain foods, insect stings, etc. and is referred to as an
allergen.for example
• Anaphylaxis:is a severe whole-body allergic reaction
• that occurs within minutes of exposure, progresses
rapidly and can lead to anaphylactic shock and death.

3. 1-Food Allergy(Epinephrine)
2-Skin Allergy (Hydrocortisone
cream).
3-Dust Allergy( fexofenadine )
4-Insect Sting Allergy(calmine lotion)
5-Pet Allergies(cetirizine (Zyrtec),
diphenhydramine (Benadryl),
6-Eye Allergy(fexofenadine (Allegra)
7-Drug Allergies(diphenhydramine
(Benadryl)
8-Allergic Rhinitis
9-Latex Allergy
10-Mold Allergy

4. • A person is exposed to an allergen by inhaling it, swallowing it, or
getting in on their skin. After a person is exposed, there is a
sequence of events that create an allergic reaction:
• The body produces an antibody, IgE, to bind the allergen. These
antibodies attach to a mast cell, which can be found in the airways,
intestines, and elsewhere Allergens bind to the IgE, which is
attached to the mast cell, which causes the mast cells to release a
variety of chemicals into the blood such as histmamine. Histamine
causes most of the symptoms of an allergic reaction.

5. Allergic Reaction

7. • There is skin testing, as well as allergy blood tests. Skin tests give fast
results and usually cost less than blood tests. Blood tests are helpful
because it only involves a single needle prick, however it costs more.
All test results must be interpreted with the medical history.
• There are two types of allergy treatment:
1. Medication: and are the most
common. They help to reduce a stuffy nose, runny nose,
sneezing or itching. Corticosteroids treat inflammation in the
nose.
2. Immunotherapy:A preventive treatment for allergic reactions
that involves giving gradual increase doses of the allergen.
The slow increase of the allergen allows the immune system
to become less sensitive to the allergen.

8. • Chemical messenger that mediates a wide range of
cellular responses, including allergic and
inflammatory reactions, gastric acid secretion, and
neurotransmission in parts of the brain.
• Plays an important role in gastric acid secretion.
• Histamine is a major mediator of allergic and
inflammatory processes.

9. Location of Histamine
• Histamine is a biogenic amine found in many
tissues, including mast cells, basophils,
lymphocytes, neurons, and gastric
enterochromaffin-like cells.
• High amounts found in lung, skin, and the GIT.
• Found at high concentration in mast cells or
basophils.
• Occurs as a component of venoms and in
secretions from insect stings.

10. Adverse effects of Histamine Release
• Itching, Urticaria.
• Flushing.
• Hypotension
• Tachycardia
• Bronchospasm
• Angioedema
• Wakefullness
• Increased acidity (Gastric acid secretion)

12. Biosynthesis of Histamine

13. Synthesis of Histamine
• Histamine is an amine
formed by the
decarboxylation of the
amino acid histidine by
histidine decarboxylase.

15. • Histamine synthesis and storage can be divided into two “pools”:
1. a slowly turning over pool.
2. a rapidly turning over pool.
1-The slowly turning over pool is located in mast cells and
basophils.Histamine is stored in large granules in these
inflammatory cells, and the release of histamine involves complete
degranulation of the cells.
2-The rapidly turning over pool is located in gastric ECL cells
and in histaminergic CNS neurons.These cells synthesize and
release histamine as required for gastric acid secretion and
neurotransmission, respectively.

17. Release of Histamine
A. Immunologic Release:Mast cell sensitized by IgE
antibodies attached to their surface membranes,
degranulate explosively when exposed to the
appropriate antigen
• This type of release requires energy.
• Degranulation leads to the simultaneous release of
histamine, adenosine triphosphate (ATP), and other
mediators that are stored together in the granules.
• Histamine released by this mechanism is a mediator
in immediate (type I) allergic reactions, such as hay
fever and acute urticaria.

19. Chemical and Mechanical Release
• Chemical and mechanical mast cell injury causes
degranulation and histamine release.
• Drugs such as morphine and tubocurarine, can
displace histamine from its bound form within
cells.
• This type of release does not require energy and is
not associated with mast cell injury or
degranulation.
• Loss of granules from the mast cell also releases
histamine.