4 Types of Hypersensitivity Reaction Cheat Sheet

Once you have read this section you will be familiar with the 4 main types of hypersensitivity reactions that can be produced by the immune system. You will understand and be able to distinguish between the mechanisms of damage involved in each reaction and the time taken for these reactions to occur. We have also provided you with the common clinical conditions associated with each type of hypersensitivity reaction.

Hypersensitivity reactions are a group of conditions in which the immune system, which normally serves a protective role, has a harmful effect. Both allergies and many autoimmune disorders fall under the umbrella of hypersensitivity reactions, the difference being that allergies involve an immune reaction to common substances in the environment, whereas autoimmune diseases involve a direct immune reaction to tissues within the body.
Hypersensitivity reactions are commonly classified into four types:

Type 1:

Type I hypersensitivity reactions are immediate allergic reactions some examples of type 1 hypersensitivity:
Allergic asthma
Allergic conjunctivitis
Allergic rhinitis (“hay fever”)
Atopic dermatitis (eczema)
Urticaria (hives)

Type II:

Type II hypersensitivity reactions are referred to as cytotoxic, as they involve antibodies that are specific to particular tissues within the body and cause destruction of cells in these tissues. Some examples includes:

Autoimmune hemolytic anemia
Goodpasture’s syndrome
Erythroblastosis Fetalis
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

Type III:

Type III hypersensitivity reactions are immune complex-mediated, with tissue damage caused by antigen-antibody complex deposition. Some examples are:
Immune complex glomerulonephritis
Rheumatoid arthritis
Serum sickness
Subacute bacterial endocarditis
Symptoms of malaria
Systemic lupus erythematosus
Arthus reaction
Farmer’s Lung (Arthus-type reaction)

Type IV:

Type IV hypersensitivity (e.g., TB skin tests, contact dermatitis) reactions are delayed and cell-mediated, and are the only hypersensitivity reactions that involve sensitized T lymphocytes rather than antibodies.
Some Examples of Type IV includes:
Contact dermatitis (poison ivy rash, for example)
Temporal arteritis
Symptoms of leprosy
Symptoms of tuberculosis
Transplant rejection
Coeliac disease

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