ICOS

ICOS, inducible T-cell costimulatory molecule, alias CD278, AILIM, is a type I transmembrane glycoprotein belonging to the CD28 family of costimulatory immunoreceptors, which is usually rapidly up-regulated and expressed upon T-cell activation.
The mechanism of action of ICOS involves interactions with its unique ligand (ICOS-L) on antigen-presenting cells (APCs), which triggers intracellular signaling cascades through conserved intracellular motifs, such as YMFM, IProx, and KKKY, to promote T cell activation and differentiation. ICOS plays a key role in the regulation of adaptive immune responses, and is particularly critical in T helper cell (Tfh) formation and humoral immune responses. Defects in the ICOS gene result in a severely impaired humoral immune response.
In addition, ICOS affects Th1, Th2 and Th17 immune responses as well as regulatory T cell (Treg) homeostasis. Regulation of the ICOS/ICOS-L signaling pathway has great potential in cancer immunotherapy and autoimmune disease treatment.