Hypersensitivity-Immune Complex

Hypersensitivity-Immune Complex mediated disease:

Definition:

Immune complex mediated reactions are started by antigen-antibody [i.e., immune] complexes which either are formed locally at the site of tissue damage or are deposited there from circulation.

Types & Examples:

Arthus reaction and Serum Sickness are illustrations of type III hypersensitivity reactions.

1. Arthus Reaction:

In the year 1903, Arthus noticed this reaction in rabbits whenever they were injected subcutaneously with horse serum. Preliminary injections were without any local effect, however with later injections, induration, edema, and hemorrhagic necrosis outcome. This is termed as Arthus reaction.

Mechanism of Arthus reaction:

Whenever an antigen is injected intradermally it joins with antibody in the serum to made antigen-antibody complexes [i.e., Immune complex]. Such immune complexes activate complement. Complement causes mast cell degranulation and attract neutrophils into tissue. Since an outcome of mast cell degranulation vasoactive amines like histamine & leucotrienes are liberated. These raise the blood flow and capillary permeability. Lysosomal enzymes cause inflammation of the blood vessel endothelial membrane. As an outcome of accumulation of immune complexes little thrombi are viewed in blood vessels that cause reduced blood supply and go ahead to tissue necrosis.

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Figure: Mechanism of Arthus Reaction


2. Serum Sickness:

  • Serum sickness was explained by Von Pirquet and Schick in the year 1905.
  • This appeared in 7 to 12 days following a single injection of a high concentration of foreign serum.
  • The clinical syndrome comprises of fever, spleenomegaly, arthritis, glomerulonephritis rashes and so forth.

 

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