Type III hypersensitivity
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Type III hypersensitivity
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IgG antibodies p. 103
in type III hypersensitivity reactions p. 111
Type III hypersensitivity p. 111
C3 deficiency and p. 105
organ transplants p. 117
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Transcript
Content Reviewers
Rishi Desai, MD, MPHContributors
Tanner Marshall, MS
Having a hypersensitivity means that someone’s immune system has reacted to something in a way that ends up damaging them, as opposed to protecting them.
There are four different hypersensitivities and the third type or type III hypersensitivity reaction happens when antigen-antibody complexes deposit in blood vessel walls, causing inflammation and tissue damage.
Alright so first off, type III hypersensitivity reactions are mediated by immune complexes. Immune complexes, aka antigen-antibody complexes are made of two parts—the antigen and the antibody.
Antibodies, sometimes called immunoglobulins, are produced by plasma cells, which are basically fully matured and differentiated B cells.
Initially these cells make IgM - which can be secreted or bound to the plasma cell surface where it acts as a B cell receptor.
When a B cell undergoes cross-linking of two surface bound IgMs, it then takes up the antigen and presents a piece of it to T helper cells via t cell receptor to the MHC- class II molecule presenting the piece of antigen, along with costimulatory molecule CD4.
The B cell’s CD40 also binds to the T cell’s CD40 ligand, and then the t cell releases cytokines, which results in b cell activation and class switching, or isotype switching, where it changes the type of antibodies it makes.
In type III hypersensitivity reactions, typically B cells will switch from making IgM to making IgG antibodies.
Now remember that all antibodies are specific, right? Meaning that they recognize specific molecules called antigens, the second part of immune complexes.
Summary
Type III hypersensitivity is a type of immune response in which antigen-antibody complexes accumulate in the tissues and cause inflammation and tissue damage. This type of hypersensitivity is also known as immune-complex-mediated hypersensitivity. Examples of Type III hypersensitivity reactions include systemic lupus erythematosus, rheumatoid arthritis, and serum sickness. Symptoms can vary depending on the tissues affected and may include joint pain and swelling, rashes, fever, and kidney damage. Treatment options may include removing the triggers, and medications like antihistamines, nonsteroidal anti-inflammatory drugs, and corticosteroids.
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