HYPERSENSITIVITY REACTIONS TYPES

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Gell-Coombs classification of Hypersensitivity

Type 1 – IgE mediated Hypersensitivity / Immediate type Hypersensitivity/Atopic type Hypersensitivity.








Examples:

Allergic asthma

Allergic conjunctivitis

Allergic rhinitis (“hay fever”)

Anaphylaxis

Angioedema

Atopic dermatitis (eczema)

Urticaria (hives)

Eosinophilia

Type 2 Hypersensitivity reaction

Type 2 Hypersensitivity reaction-Antiboy mediated cellular cytotoxicity

In case of type 2 hypersensitivity reactions, Antibodies tend to bind the antigen on the cell surface. These antigens can be either be intrinsic (“self” antigen, innately part of the patient’s cells) or extrinsic (absorbed onto the cells during exposure to some foreign antigen, possibly as part of infection with a pathogen).


IgG and IgM antibodies bind to these antigens to form complexes that activate the classical pathway of complement activation, for eliminating cells presenting foreign antigens (which are usually, but not in this case, pathogens).

Examples:

Autoimmune hemolytic anemia

Goodpasture’s syndrome

Erythroblastosis Fetalis

Pemphigus

Pernicious anemia (if autoimmune)

Immune thrombocytopenia

Transfusion reactions

Hashimoto’s thyroiditis

Graves’ disease (see type V below)

Myasthenia gravis (see type V below)

Rheumatic fever

Hemolytic disease of the newborn

What is type 5 hypersensitivity reaction?

It is a variation of type 2 hypersensitivty reaction where the  antibody has a stimulatory effect.

e.g. Graves disease

Type 3 Hypersensitivity reaction- Immune complex reaction

In this case the IgG and IgM antibodies bind the antigens forming soluble immune complexes that get deposited in the various tissues of our body like kidney, skin, joints.

Examples:

Post streptococcal Glomerulonephritis

Rheumatoid Arthritis

Serum sickness

SLE

Subacute bacterial endocarditis

Symptoms of malaria

Systemic lupus erythematosus

Arthus reaction

Farmer’s Lung (Arthus-type reaction)

What is Arthus reaction?

It is a type of type 3 hypersensitivity reaction that occurs after intradermal injection of an antigen leading to antigen-antibody reaction.

Arthur reaction is a local vasculitis associated with deposition of immune complexes and activation of complement.

It has been associated with diphtheria and tetanus vaccination.

Type 4 Hypersensitivity reaction

Also known as Cell mediated hypersensitivity/Delayed type Hypersensitivity

It is not an antibody mediated hypersensitivity reaction.

It is cell mediated and takes 2-3 days after exposure to develop the reaction.



Examples:

Contact dermatitis (poison ivy rash, for example)

Temporal arteritis

Symptoms of leprosy

Symptoms of tuberculosis

Transplant rejection

Coeliac disease


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