Editing Immune system (section)

=== Hypersensitivity ===
{{further|Hypersensitivity}}
[[Hypersensitivity]] is an immune response that damages the body's own tissues. It is divided into four classes (Type I&nbsp;– IV) based on the mechanisms involved and the time course of the hypersensitive reaction. Type I hypersensitivity is an immediate or [[anaphylaxis|anaphylactic]] reaction, often associated with allergy. Symptoms can range from mild discomfort to death. Type I hypersensitivity is mediated by [[immunoglobulin E|IgE]], which triggers degranulation of [[mast cell]]s and [[basophil granulocyte|basophils]] when cross-linked by antigen.<ref name="USCH">{{cite web|url=http://www.microbiologybook.org/book/immunol-sta.htm|title=Immunology&nbsp;– Chapter Seventeen: Hypersensitivity States| vauthors = Ghaffar A |year=2006|publisher=University of South Carolina School of Medicine|work=Microbiology and Immunology On-line|access-date=29 May 2016}}</ref>
Type II hypersensitivity occurs when antibodies bind to antigens on the individual's own cells, marking them for destruction. This is also called antibody-dependent (or cytotoxic) hypersensitivity, and is mediated by [[immunoglobulin G|IgG]] and [[immunoglobulin M|IgM]] antibodies.<ref name=USCH /> [[Immune complex]]es (aggregations of antigens, complement proteins, and IgG and IgM antibodies) deposited in various tissues trigger Type III hypersensitivity reactions.<ref name=USCH /> Type IV hypersensitivity (also known as cell-mediated or ''delayed type hypersensitivity'') usually takes between two and three days to develop. Type IV reactions are involved in many autoimmune and infectious diseases, but may also involve [[contact dermatitis]]. These reactions are mediated by [[T cell]]s, [[monocyte]]s, and [[macrophage]]s.<ref name=USCH />