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16: Hypersensitivities

Last updated

Apr 9, 2022
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- 15.E: Immunodeficiency (Exercises)
- 16.1: Immediate Hypersensitivities: Type I

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Hypersensitivities are a set of undesirable reactions produced by the normal immune system, including allergies and autoimmunity. These reactions may be damaging, uncomfortable, or occasionally fatal. Hypersensitivity reactions require a pre-sensitized (immune) state of the host. Immediate hypersensitivities refer to humoral immunity (antigen/antibody reactions) causing harm. Delayed hypersensitivities refer to cell-mediated immunity (cytotoxic T-lymphocytes, macrophages, and cytokines) leading to harm.

Topic hierarchy

16.1: Immediate Hypersensitivities: Type I
Immediate hypersensitivities refer to humoral immunity (antigen/antibody reactions) causing harm. During Type I (IgE mediated or anaphylactic-type) hypersensitivity, IgE is made in response to an allergen. In allergic individuals, the levels of IgE may be thousands of times higher than in those without allergies.
16.2: Immediate Hypersensitivities: Type II
During type II (antibody-dependent cytotoxicity) hypersensitivity, either IgG or IgM is made against normal self antigens as a result of a failure in immune tolerance, or a foreign antigen resembling some molecule on the surface of host cells enters the body and IgG or IgM made against that antigen then cross reacts with the host cell surface.
16.3: Immediate Hypersensitivities: Type III
Type III (immune complex-mediated) hypersensitivity is caused when soluble antigen-antibody (IgG or IgM) complexes, which are normally removed by macrophages in the spleen and liver, form in large amounts and overwhelm the body. These small complexes lodge in the capillaries, pass between the endothelial cells of blood vessels - especially those in the skin, joints, and kidneys - and become trapped on the surrounding basement membrane beneath these cells.
16.4: Immediate Hypersensitivities - Type V
Type V (Stimulatory Hypersensitivity) invovles making Antibodies are made against a particular hormone receptor on a hormone-producing cell. This leads to the overstimulation of those hormone-producing cells. An example is Graves' disease where antibodies are made against thyroid-stimulating hormone receptors of thyroid cells. The binding of the antibodies to the TSH receptors results in constant stimulation of the thyroid leading to hyperthyroidism.
16.5: Delayed Hypersensitivities - Type IV
During delayed hypersensitivity, T8-lymphocytes become sensitized to an antigen and differentiate into cytotoxic T-lymphocytes, while effector T4-lymphocytes become sensitized to an antigen and produce cytokines. CTLs, cytokines, eosinophils, and/or macrophages then cause harm rather than benefit.
16.6: Superantigens
Conventional antigens are only recognized by specific T4-cells having a TCR with a corresponding shape. Superantigens are unusual bacterial toxins that interact with exceedingly large numbers of T4-lymphocytes. Activation of very large numbers of T4-lymphocytes results in the secretion of excessive amounts of a cytokine called interleukin-2 (IL-2).
16.E: Hypersensitivities (Exercises)
These are homework exercises to accompany Kaiser's "Microbiology" TextMap. Microbiology is the study of microorganisms, which are defined as any microscopic organism that comprises either a single cell (unicellular), cell clusters or no cell at all (acellular). This includes eukaryotes, such as fungi and protists, and prokaryotes. Viruses and prions, though not strictly classed as living organisms, are also studied.

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