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Co-stimulation is a secondary signal which immune cells rely on to activate an immune response in the presence of an antigen-presenting cell. [1] In the case of T cells, two stimuli are required to fully activate their immune response.
The signal transduction mechanism by which a T cell elicits this response upon contact with its unique antigen is termed T-cell activation. Upon binding to pMHC, the TCR initiates a signaling cascade, involving transcription factor activation and cytoskeletal remodeling resulting in T-cell activation.
Once a T cell has been appropriately activated (i.e. has received signal one and signal two) it alters its cell surface expression of a variety of proteins. 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).
Once the two-signal activation is complete the T helper cell (T h) then allows itself to proliferate. It achieves this by releasing a potent T cell growth factor called interleukin 2 (IL-2) which acts upon itself in an autocrine fashion.
It is composed of four distinct chains. In mammals, the complex contains a CD3γ chain, a CD3δ chain, and two CD3ε chains. These chains associate with the T-cell receptor (TCR) and the CD3-zeta (ζ-chain) to generate an activation signal in T lymphocytes. The TCR, CD3-zeta, and the other CD3 molecules together constitute the TCR complex.
This activation of naive T cell is controlled by a variety of signals: recognition of antigen in the form of a peptide: MHC complex on the surface of a specialized antigen-presenting cell delivers signal 1; interaction of co-stimulatory molecules on antigen-presenting cells with receptors on T cells delivers signal 2 (one notable example ...
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 ...
Both coreceptor-bound and free Lck can phosphorylate the CD3 chains upon TCR activation, evidences suggest that the free form of Lck can be recruited and trigger the TCR signal faster than the coreceptor-bound Lck [7] Additionally, upon T cell activation, a fraction of kinase active Lck, translocate from outside of lipid rafts (LR) to inside ...