This document summarizes different types of hypersensitivity reactions. It defines hypersensitivity reactions as abnormal immune responses that cause physiological or histological damage. Hypersensitivity reactions are classified as immediate or delayed based on the time it takes for a clinical reaction to develop upon re-exposure to an antigen. The document distinguishes between immediate and delayed hypersensitivity reactions and provides examples of each. It then summarizes Coombs and Gell's classification of hypersensitivity reactions into five types based on pathogenic mechanisms and provides examples of each type. Finally, it compares the characteristics of type I, II, III and IV hypersensitivity reactions.

1. HYPERSENSITIVITY REACTIONS

2. Introduction
• Hypersensitivity reaction can be described as an abnormal immune response
which produces the physiological or histopathological damage in the host agents.
• On the basis of the time required to develop clinical reactions on re-exposure to
antigens, hypersensitvity reactions are classified as Immediate and Delayed types.
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3. Distinguish between Immediate hypersensitivity and Delayed
hypersensitivity
Sr.no
.
Immediate hypersensitivity Delayed hypersensitivity
1 It appears rapidly. It appears slowly.
2 Reaction develop in less than 12
hours.
Reaction develop in 24 to 48 hours.
3 Lesions are acute, exudation and fat. Mononuclear cell collection around blood vessels.
4 It is induced by antigens or haptens. It is induced by infection, injection of antigens or
haptens.
5 Passive transfer possible with serum. Passive transfer possible with T- lymphocytes.
6 Desensitization is easy but short
lived.
It is quite difficult but long lasting.
7 Circulating antibodies present. Circulating antibodies are absent.
8 It remains for shorter time. It remains for longer time.
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4. • Coombs and Gell (1963) classified hypersensitivity reactions into five types
based on the different mechanisms of pathogenesis which are as follows:
Sr.no. Types of hypersensitivity reaction Examples
1 Type I ( Anaphylactic, immediate,
IgE or reagin dependent)
Anaphylaxis, Atopy, etc.
2 Type II ( Cytotoxic or cell
stimulating)
Thrombocytopenia, haemolytic
anaemia, etc.
3 Type III (Immuno complex, toxic
complex)
Arthus reaction, serum sickness,etc.
4 Type IV ( Delayed or T-cell
mediated)
Tuberculin type, contact dermatitis,
etc.
5 Type V ( Stimulatory or
antireceptor)
Autoimmune orchitis in guinea pigs.
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5. Comparison of hypersensitivity reactions
Characteristics Type I Type II Type III Type IV
Antibody involved IgE IgM,IgE IgG, IgM T- cells
Type of reaction Immediate Cytotoxic Immune complex Delayed
Antigen soluble or
particulate
On cell surface soluble or
particulate
On cell surface
Reaction time In sec or minutes In hours 4 to 8 hours 24 to 48 hours
Nature of reaction Local, wheal or flare Clumping of RBC Acute inflammation Cell mediated cell
destruction
Therapy Desensitization Steriods Steriods Steriods
Reaction mediators Mast cells
Eosinophils
Anaphylactic factors
Complement Eosinophils
Neutrophils
Complement
Macrophages
Lymphokines
Examples Hay fever
Asthma
Food and insect
allergies
Agranulocytosis
Thrombocytopenia
Haemolytic anaemia
Blood reaction
Arthus reaction
Serum sickness
Golmeruler
nephritis
Tuberculosis
Contact dermatitis
Graft rejection
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