Type IV hypersensitivity

Type IV hypersensitivity
Video explanation
Classification and external resources
MeSH D006968

Type 4 hypersensitivity is often called delayed type hypersensitivity as the reaction takes two to three days to develop. Unlike the other types, it is not antibody mediated but rather is a type of cell-mediated response.

CD4+ helper T cells recognize antigen in a complex with MHC II major histocompatibility complex on the surface of antigen-presenting cells. These can be macrophages that secrete IL-12, which stimulates the proliferation of further CD4+ Th1 cells. CD4+ T cells secrete IL-2 and interferon gamma, inducing the further release of other Th1 cytokines, thus mediating the immune response. Activated CD8+ T cells destroy target cells on contact, whereas activated macrophages produce hydrolytic enzymes and, on presentation with certain intracellular pathogens, transform into multinucleated giant cells.

Examples

Disease Target antigen Effects
allergic contact dermatitis[1] environmental chemicals (e.g., urushiol from poison ivy

oak, nickel)

epidermal necrosis, inflammation, skin rash and blisters

autoimmune myocarditis[1] myosin heavy chain protein cardiomyopathy
diabetes mellitus type 1[1] pancreatic beta cell proteins
(possibly insulin, glutamate decarboxylase)

Insulitis, beta cell destruction

granulomas[2] various, depending on underlying disease walled off lesion containing macrophages and other cells
some peripheral neuropathies Schwann cell antigen

neuritis, paralysis

Hashimoto's thyroiditis[1] thyroglobulin antigen

hypothyroidism, hard goiter, follicular thymitis

inflammatory bowel disease[1] enteric microbiota and/or self antigens hyperactivation of T-cells, cytokine release, recruitment of macrophages and other immune cells, inflammation
multiple sclerosis[1] myelin antigens (e.g., myelin basic protein) myelin destruction, inflammation
rheumatoid arthritis[1] possibly collagen and/or citrullinated self proteins chronic arthritis, inflammation, destruction of articular cartilage and bone
tuberculin reaction

(Mantoux test)[3]

 tuberculin

induration and erythema around injection site indicates previous exposure

An example of a TB infection that came under control: M. tuberculosis are engulfed by macrophages after being identified as foreign, but due to an immuno-escape mechanism peculiar to mycobacteria, TB bacteria are able to block the fusion of their enclosing phagosome with lysosomes which would destroy the bacteria. Thereby TB can continue to replicate within macrophages. After several weeks, the immune system somehow [mechanism as yet unexplained] ramps up and, on stimulation with IFN-gamma, the macrophages become capable of killing M. tuberculosis by forming phagolysosomes and nitric oxide radicals. However the hyper-activated macrophages secrete TNF which recruits multiple monocytes into the battle. These cells differentiate into epithelioid histiocytes which wall off the infected cells, but at the cost of significant inflammation and local damage.

Some other clinical examples:

See also

References

  1. 1 2 3 4 5 6 7 Kumar, Vinay; Abbas, Abul K.; Aster, Jon C. (2012-05-01). Robbins Basic Pathology. Elsevier Health Sciences. ISBN 1455737879.
  2. ↑ "Hypersensitivity reactions". www.microbiologybook.org. University of South Carolina School of Medicine - Microbiology and Immunology On-line. Retrieved 2016-05-29.
  3. ↑ "Hypersensitivity reactions". www.microbiologybook.org. Retrieved 2016-05-29.
  4. ↑ "eMedicine - Hypersensitivity Reactions, Delayed : Article by Walter Duane Hinshaw".
This article is issued from Wikipedia - version of the 8/18/2016. The text is available under the Creative Commons Attribution/Share Alike but additional terms may apply for the media files.