hypersensitivity

Examples of hypersensitivity in the following topics:

• Hypersensitivity

  • A hypersensitivity reaction refers to an overreactive immune system triggered by allergies and autoimmunity.
  • Hypersensitivity (also called hypersensitivity reaction) refers to undesirable reactions produced by the normal immune system, including allergies and autoimmunity, and are commonly mediated by antibodies.
  • Hypersensitivity reactions require a pre-sensitized (immune) state of the host .
  • Cytotoxic Hypersensitivity (Type II) is an immune response to human cells with foreign antigens.
  • The common effects of Poison Ivy are the result of Type IV hypersensitivity.

• Type II (Cytotoxic) Reactions

  • In type II hypersensitivity (or cytotoxic hypersensitivity), the antibodies produced by the immune response bind to antigens on the patient's own cell surfaces.
  • Another form of type II hypersensitivity is called antibody-dependent cell-mediated cytotoxicity (ADCC).
  • Autoimmune diseases resemble type II-IV hypersensitivity reactions.
  • They differ from hypersensitivity reactions in that the antigens driving the immune process are self-antigens rather than non-self as in hypersensitivity reactions.
  • Below are some examples of Type II hypersensitivity-like autoimmunity.

• Hypersensitivities

  • Hypersensitivities are maladaptive immune reactions against harmless antigens (allergies) or against self antigens (autoimmunity).
  • The types of hypersensitivities include immediate, delayed, and autoimmunity hypersensitivities.
  • A large proportion of the population is affected by one or more types of hypersensitivity.
  • This type of hypersensitivity involves the TH1 cytokine-mediated inflammatory response.
  • Delayed hypersensitivity occurs in some individuals in response to contact with certain types of jewelry or cosmetics.

• Allergies

  • An allergy is a hypersensitivity disorder of the immune system.
  • Allergy is one of four forms of hypersensitivity and is formally called type I (or immediate) hypersensitivity.
  • If an immuno-response is seen, it can be concluded that the patient has a hypersensitivity (or allergy) to that allergen.

• Type III (Immune Complex) Reactions

  • Type III hypersensitivity occurs when there is little antibody and an excess of antigen, leading to the formation of small immune complexes.
  • It is characterized by solvent antigens that are not bound to cell surfaces (which is the case in type II hypersensitivity).
  • Hence, vasculitis, glomerulonephritis and arthritis are commonly-associated conditions as a result of type III hypersensitivity responses.
  • Skin response to a hypersensitivity of this type is referred to as an Arthus reaction, and is characterized by local erythema and some induration.
  • This is the third form of hypersensitivity in the Gell-Coombs classification, called Type III hypersensitivity.

• Type I (Anaphylactic) Reactions

  • Type I (or immediate/anaphylactic) hypersensitivity can be caused by the body's response to a foreign substance.
  • Type I hypersensitivity is also known as immediate or anaphylactic hypersensitivity.

• Immune Complex Autoimmune Reactions

  • This is the third form of hypersensitivity in the Gell-Coombs classification, called Type III hypersensitivity.
  • In immunology, the Arthus reaction is a type of local type III hypersensitivity reaction.
  • Type III hypersensitivity reactions are immune complex-mediated.
  • Typical of most mechanisms of the type III hypersensitivity, Arthus manifests as local vasculitis due to deposition of IgG-based immune complexes in dermal blood vessels.

• Type IV (Delayed Cell-Mediated) Reactions

  • Type IV hypersensitivity reactions are cell-mediated and take 2 to 3 days to develop.
  • Type IV hypersensitivity is often called delayed type hypersensitivity as the reaction takes two to three days to develop.
  • A classic example of delayed type IV hypersensitivity is the Mantoux tuberculin test in which skin induration indicates exposure to tuberculosis.

• Plant Defenses Against Pathogens

  • A hypersensitive response, in which the plant experiences rapid cell death to fight off the infection, can be initiated by the plant; or it may use endophyte assistance: the roots release chemicals that attract other beneficial bacteria to fight the infection.

• Glomerular Diseases