Editing Cell-mediated immunity (section)

==History==

In the late 19th century [[Hippocrates#Hippocratic theory|Hippocratic tradition]] medicine system, the immune system was imagined into two branches: [[humoral immunity]], for which the protective function of immunization could be found in the humor (cell-free [[bodily fluid]] or [[blood plasma|serum]]) and '''cellular immunity''', for which the protective function of immunization was associated with cells. [[CD4]] cells or [[T helper cell|helper T cell]]s provide protection against different [[pathogens]]. [[Naive T cells]], which are immature T cells that have yet to encounter an [[antigen]], are converted into activated effector [[T cell]]s after encountering [[antigen-presenting cells]] (APCs). These APCs, such as [[macrophages]], [[dendritic cells]], and [[B cells]] in some circumstances, load antigenic peptides onto the [[major histocompatibility complex]] (MHC) of the cell, in turn presenting the [[peptide]] to receptors on T cells. The most important of these APCs are highly specialized dendritic cells; conceivably operating solely to ingest and present antigens.<ref name="auto">{{Cite journal |last1=Ross Russell |first1=Amy L |last2=Dryden |first2=Matthew S |last3=Pinto |first3=Ashwin A |last4=Lovett |first4=Joanna K |date=2018-10-03 |title=Lyme disease: diagnosis and management |url=http://dx.doi.org/10.1136/practneurol-2018-001998 |journal=Practical Neurology |volume=18 |issue=6 |pages=455–464 |doi=10.1136/practneurol-2018-001998 |pmid=30282764 |s2cid=52915054 |issn=1474-7758|url-access=subscription }}</ref> Activated effector T cells can be placed into three functioning classes, detecting [[peptide]] antigens originating from various types of [[pathogen]]: The first class being 1) [[Cytotoxic T cells]], which kill infected target cells by [[apoptosis]] without using cytokines, 2) [[T helper cell#Th1/Th2 model|T<sub>h</sub>1 cells]], which primarily function to activate macrophages, and 3) [[T helper cell#Th1/Th2 model|T<sub>h</sub>2 cells]], which primarily function to stimulate [[B cells]] into producing [[antibodies]].<ref name="auto"/>

In another ideology, the [[innate immune system]] and the [[adaptive immune system]] each comprise both [[humoral immunity|humoral]] and cell-mediated components. Some cell-mediated components of the innate immune system include myeloid [[phagocyte]]s, innate lymphoid cells ([[NK cell]]s) and [[intraepithelial lymphocyte]]s.<ref>{{Cite journal|last1= Romo |first1=MR |last2=Pérez-Martínez |first2=D |last3=Ferrer |first3=CC |year=2016 |title= Innate immunity in vertebrates: an overview|journal=Immunology |volume= 148|issue=2 |pages=125–139|doi= 10.1111/imm.12597|pmid=26878338 |pmc=4863567 |s2cid=35251844 |language=en}}</ref>