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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.
Subsequently, the primed cells will differentiate either into effector cells or into memory cells that can mount stronger and faster response to second and upcoming immune challenges. [2] T and B cell priming occurs in the secondary lymphoid organs (lymph nodes and spleen). Priming of naïve T cells requires dendritic cell antigen presentation.
CD2 was shown to prime naive T cells (T N) even without CD28 or TCR. [2] Also, CD27 is a receptor constitutively expressed on T N (its expression is downregulated upon TCR stimulation) and enhances T cell proliferation. [9] The differentiation of T helper cells (T H) into different subsets also partially depends on their co-stimulatory molecules.
The process of formation begins when the T-cell receptor binds to the peptide:MHC complex on the antigen-presenting cell and initiates signaling activation through formation of microclusters/lipid rafts. Specific signaling pathways lead to polarization of the T-cell by orienting its centrosome toward the site of the immunological synapse. The ...
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.
The Lck is a member of Src kinase family (SFK) and is important for the activation of T-cell receptor (TCR) signaling in both naive T cells and effector T cells. The role of Lck is less prominent in the activation or in the maintenance of memory CD8 T cells in comparison to CD4 T cells.
ITAMs are important for signal transduction, mainly in immune cells. They are found in the cytoplasmic tails of non-catalytic tyrosine-phosphorylated receptors [7] such as the CD3 and ζ-chains of the T cell receptor complex, the CD79-alpha and -beta chains of the B cell receptor complex, and certain Fc receptors.
On a population level, T-cell activation depends on the strength of TCR stimulation, the dose–response curve of ligand to cytokine production is sigmoidal. However, T-cell activation on a single cell level can be characterized by a digital switch-like response, meaning the T cell is fully activated if the stimulus is higher than a given ...