Editing T helper cell (section)

== Structure and function ==

T<sub>h</sub> cells contain and release cytokines to aid other immune cells. Cytokines are small protein mediators that alter the behavior of target cells that express [[Receptor (biochemistry)|receptors]] for those cytokines. These cells help polarize the immune response depending on the nature of the immunological insult (for example; virus vs. extracellular [[Bacteria|bacterium]] vs. intracellular bacterium vs. [[Parasitic worm|helminth]] vs. fungus vs. protist).{{cn|date=February 2024}}

Mature T<sub>h</sub> cells express the surface protein [[CD4]] and are referred to as '''CD4<sup>+</sup> T cells'''. CD4<sup>+</sup> T cells are generally treated as having a pre-defined role as helper T cells within the [[immune system]]. For example, when an [[antigen-presenting cell]] displays a [[peptide]] antigen on [[MHC class II]] proteins, a CD4<sup>+</sup> cell will aid those cells through a combination of cell to cell interactions (e.g. [[CD40 (protein)]] and [[CD154|CD40L]]) and through [[cytokines]].{{cn|date=April 2025}}

T<sub>h</sub> cells are not a monolithic immunological entity because they are diverse in terms of function and their interaction with partner cells. In general, mature naive T cells are stimulated by professional antigen presenting cells to acquire an effector function. These are defined by the presence of a lineage-determining (or lineage-specifying) transcription factor (also called [[master regulator]], though the term has been criticized for being too reductive).<ref>{{cite journal | vauthors = Oestreich KJ, Weinmann AS | title = Master regulators or lineage-specifying? Changing views on CD4+ T cell transcription factors | journal = Nature Reviews. Immunology | volume = 12 | issue = 11 | pages = 799–804 | date = November 2012 | pmid = 23059426 | pmc = 3584691 | doi = 10.1038/nri3321 }}</ref> The loss of function in a lineage specifying transcription factor results in the absence of the corresponding class of helper T cell which can be devastating for the health of the host.{{cn|date=April 2025}}