Hypersensitivity

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Hypersensitivity
Classification and external resources
ICD-10T78.4
ICD-9995.3
DiseasesDB28827
MeSHD006967
 
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Hypersensitivity
Classification and external resources
ICD-10T78.4
ICD-9995.3
DiseasesDB28827
MeSHD006967

Hypersensitivity (also called hypersensitivity reaction or intolerance) refers to 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. The four-group classification was expounded by P. H. G. Gell and Robin Coombs in 1963.[1]

Coombs and Gell classification[edit]

Comparison of hypersensitivity types
TypeAlternative namesOften mentioned disordersMediatorsDescription
IAllergy (immediate)Fast response which occurs in minutes rather than multiple hours or days. Free antigens cross link the IgE on mast cells and basophils which causes a release of vasoactive biomolecules.

Testing can be done via skin test for specific IgE.[2]

IICytotoxic, antibody-dependentAntibody (IgM or IgG) binds to antigen on foreign cell leading to cellular destruction via the MAC.

Testing includes both the direct and indirect Coombs test.[3]

IIIImmune complex diseaseAntibody (IgG) binds to antigen on foreign cell leading to cellular destruction via neutrophils and the subsequent release of lysosomal enzymes.[4]
IVDelayed-type hypersensitivity[2][3](DTH), cell-mediated immune memory response, antibody-independentT cells find antigen and activate macrophages.[4]
VAutoimmune disease, receptor mediated (see below)

Type V[edit]

This is an additional type that is sometimes (often in the UK) used as a distinction from Type 2.[6]

Instead of binding to cell surface components, the antibodies recognise and bind to the cell surface receptors, which either prevents the intended ligand binding with the receptor or mimics the effects of the ligand, thus impairing cell signaling.

Some clinical examples:

The use of Type 5 is rare. These conditions are more frequently classified as Type 2, though sometimes they are specifically segregated into their own subcategory of Type 2.

References[edit]

  1. ^ Gell PGH, Coombs RRA, eds. Clinical Aspects of Immunology. 1st ed. Oxford, England: Blackwell; 1963.
  2. ^ a b Black, CA. Delayed Type Hypersensitivity: Current Theories with an Historic Perspective Dermatol. Online J. (May 1999) 5(1):7 at http://dermatology.cdlib.org/DOJvol5num1/reviews/black.html
  3. ^ a b http://emedicine.medscape.com/article/136118-overview
  4. ^ a b Le, Tau. First Aid for the USMLE Step 1 2013, p. 203-204
  5. ^ Table 5-1 in:Mitchell, Richard Sheppard; Kumar, Vinay; Abbas, Abul K.; Fausto, Nelson (2007). Robbins Basic Pathology. Philadelphia: Saunders. ISBN 1-4160-2973-7.  8th edition.
  6. ^ Rajan TV (July 2003). "The Gell-Coombs classification of hypersensitivity reactions: a re-interpretation". Trends Immunol. 24 (7): 376–9. doi:10.1016/S1471-4906(03)00142-X. PMID 12860528. 

External links[edit]