This document summarizes the four main types of hypersensitivity or allergic reactions: 1. Type I or anaphylactic reactions involve IgE antibodies and mast cells/basophils, causing rapid reactions like hives, asthma, or anaphylactic shock. 2. Type II or cytotoxic reactions involve IgG and IgM binding to antigens on cells, destroying cells like in blood transfusions. 3. Type III or immune complex reactions occur when antigen-antibody complexes deposit in tissues, causing inflammation like glomerulonephritis. 4. Type IV or cell-mediated reactions involve T-cells and cause delayed reactions like contact dermatitis or tuberculosis skin tests.

1. Hypersensitivity
Muhammad Iqbal
Lecturer
KMU

2. Introduction
• Hypersensitivity is overreaction to an allergen.
• Or it is an antigenic response beyond that is
considered normal.
• It is also known as allergy.
• Hypersensitivity occurs when a sensitized
person re-exposes to the allergen.
• Allergy -- 4 types

3. Type 1(Anaphylactic) Reaction
• quickly developing (2—30 min) after contact of Ag
(allergen) with Ab after previous exposition.
• IgE produced in response to an antigen like insect
venom or plant pollen grains, bind to the surface of
mast cells and basophils
• mediated through histamine, leukotriens,
prostaglandins released by mast cells & basophils.
• increase of vascular permeability, vasodilatation,
bronchoconstriction, increased mucoproduction

4. • Local reaction - skin or mucosa
• Bee sting, food allergy, hay fever (pollinosis),
asthma, urticaria (hives)
• Systemic reaction ( Anaphylactic shock)
• Parenteral administration of Ag (e.g. penicillin)
• Within minutes-- itching, redding of skin,
breathing problems, abdominal pain, vomiting,
diarrhea.
• During several min -- death may occur due to
collapse of circulation (drop in blood pressure)

5. Type II (Cytotoxic) reaction
• Antigens –
• IgG and IgM are involved
• Incompatible blood transfusion -- destruction
of RBCs
• Rh-incompatibility - erythroblastosis fetalis
(anti-Rh Ab)

6. Type III (Immune Complex ) Reaction
• Formation of Ag-Ab complexes (immune complexes)
• Ag-Ab complexes are deposited in organs
• IgG is usually involved
• Acute inflammation of tissues and organs
• e.g- repeated exposure to animal serum (antitetanic)
• Vessel wall -- thrombosis - ischemic necrosis
• Manifestation …….. 2—8 hours
• For example
• Glomerulonephritis
• systemic lupus erythematosus (SLE)

7. Type IV (cell mediated) Reaction
• Cellular immunity --- T-cells
• e.g. tuberculin reaction - Mantoux test,
• Similarly IDDM…
• person previously exposed to TBC develops after
intradermal injection of Ag skin induration
• manifestation in 1-3 days .

8. Transplantation rejection
• Transplantation:
• - autologous (own tissue)
• - homologous - Other human tissue
• - heterologous - animal tissue (e.g, pig skin)
• Contact dermatitis is another example