ICOS (gene)
protein-coding gene in the species Homo sapiens
Inducible T-cell costimulator (also called CD278) is an immune checkpoint protein that in humans is encoded by the ICOS (Inducible T-cell COStimulator) gene.
The protein belongs to the CD28 and CTLA-4 cell-surface receptor family. These are proteins expressed on the surface of immune cells that mediate signalling between them. A surface protein, the ligand, binds specifically to its receptor on another cell, leading to a signalling cascade in that cell.
Function
ICOS is a receptor protein expressed on the surface of activated T cells. Its ligand ICOS-L (previously called B7RP-1) is constitutively expressed on B cells. Stimulation of the ICOS receptor on T cells by ICOS-L on B cells is required for the development of follicular helper T (Tfh) cells.
ICOS forms homodimers and plays an important role in cell-cell signaling, immune responses and regulation of cell proliferation.
Knockout phenotype
Compared to wild-type naïve T cells, ICOS-/- T cells activated with plate-bound anti-CD3 have reduced proliferation and IL-2 secretion. The defect in proliferation can be rescued by addition of IL-2 to the culture, suggesting the proliferative defect is due either to ICOS-mediated IL-2 secretion or the activation of similar signaling pathways between ICOS and IL-2.
This brief starts where responsible research should: with the source description of “ICOS (gene)” as protein-coding gene in the species Homo sapiens. Everything that follows is an evidence route, not borrowed authority.
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The date and method of observation matter as much as the stated conclusion, especially where classification or consensus has changed. The source revision retrieved here is dated Jun 21, 2026. The linked authority identifier is Q14906890. None of the 0 selected statements returned an explicit reference.
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This entry incorporates text from “ICOS (gene)” on English Wikipedia. Contributors are listed in the page history. Text is available under the Creative Commons Attribution-ShareAlike 4.0 License. Selected authority identifiers and statements are retrieved from Wikidata under CC0; their references and qualifiers remain part of the verification path.