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Markers of T cell activation include CD69, CD71 and CD25 (also a marker for Treg cells), and HLA-DR (a marker of human T cell activation). CTLA-4 expression is also up-regulated on activated T cells, which in turn outcompetes CD28 for binding to the B7 proteins. This is a checkpoint mechanism to prevent over activation of the T cell.
The antigen Thy-1 was the first T cell marker to be identified. Thy-1 was discovered by Reif and Allen in 1964 [5] during a search for heterologous antisera against mouse leukemia cells, and was demonstrated by them to be present on murine thymocytes, on T lymphocytes, and on neuronal cells.
The activation of T lymphocytes and Natural Killer (NK) cells, both in vivo and in vitro, induces expression of CD69. This molecule, which appears to be the earliest inducible cell surface glycoprotein acquired during lymphoid activation, is involved in lymphocyte proliferation and functions as a signal-transmitting receptor in lymphocytes, including natural killer (NK) cells, and platelets ...
CD2 is a specific marker for T cells and NK cells, and can therefore be used in immunohistochemistry to identify the presence of such cells in tissue sections. The great majority of T cell lymphomas and leukaemias also express CD2, making it possible to use the presence of the antigen to distinguish these conditions from B cell neoplasms.
CTLA-4 is a coinhibitory molecule that is induced on activated T cells. Interaction between CTLA-4 and CD80/CD86 leads to delivery of negative signals into T cells and reduction of number of costimulatory molecules on the cell surface. It can also trigger a signaling pathway responsible for expression of enzyme IDO (indolamine-2,3-dioxygenase).
In turn, this results in the T cell acquiring an activated phenotype seen by the up-regulation of surface markers CD25 +, CD44 +, CD62L low, CD69 + and may further differentiate into a memory T cell. Having adequate numbers of naive T cells is essential for the immune system to continuously respond to unfamiliar pathogens.
Lymphocyte-activation gene 3, also known as LAG-3, is a protein which in humans is encoded by the LAG3 gene. [5] LAG3, which was discovered in 1990 [6] and was designated CD223 (cluster of differentiation 223) after the Seventh Human Leucocyte Differentiation Antigen Workshop in 2000, [7] is a cell surface molecule with diverse biological effects on T cell function but overall has an immune ...
Compared to wild-type naïve T cells, ICOS-/- T cells activated with plate-bound anti-CD3 have reduced proliferation and IL-2 secretion. [11] 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.