Activation of T lymphocyte is as simple as driving a car!!!!

Activation of T lymphocyte is as simple as driving a car!!!!

Image1: Mechanism of T lymphocyte activation

T lymphocytes constitute 60-70% of the peripheral blood lymphocyte. Most of the T lymphocytes has antigen specific T cell receptor(TCR),that is comprised of α and β polypeptide chains. There are various types of T cells such as-

1) Helper T cells : It helps in activation of B/T lymphocytes and macrophages.

2) Cytotoxic T cells: Involved in killing of infected cells.

3) Regulatory T cells: Causes suppression of immune response.

Now to carry out these functions a T cells needs to be activated first!

In this context, for activation of T lymphocyte, there are few structures which are present on the surface of T cells and the play the main roles in activation of T cells. They are(Image 3):

a) T cell receptor(TCR): Bind with the antigen bound to the MHC molecule on antigen presenting cells(APC).

T cell receptor

b) CD 4 or CD 8 molecule: Act as co-receptor and enhance the signal.

c) CD28 molecule: Binds to the B7-/B7-2 receptors on antigen presenting cells and act as co-stimulatory molecule.

CD 28 molecule

On the other hand, antigen presenting cells has MHC molecule for presenting the antigen to T cell and B7-1/B7-2 molecule to get attached with the CD 28 molecule on T cells.

Now coming to the most interesting part of this blog!!!!!

The activation of T cells can be compared with driving a car!

Image 2

For driving a car, first you have to  put in a key and turn on ignition(part1) and then we have to put the gear on and press the accelerator(part2).If you just complete the part 1, then the car won’t move!!! So, after ignition you must have to put on the gear and press the accelerator to move the car.

SIMILARLY, in case of T cell activation, the part 1 is binding of TCR to the MHC bound antigen on APC(Shown as signal 1 in Image3).

And the part 2 is  binding of the CD28 molecule to the B7-1/B7-2 Molecule on APC(Shown as signal 2 in image3 ).It will complete the process of activation. So, this part of co-stimulation is mandatory for successful activation. This part2 or the process of co-stimulation is vital for prevention of autoimmune disease.Because ,if by mistake, the APC present a self antigen, then this part 2 dose not take place and prevent activation of self reactive T cells!!!!

Image 3:Mechanism of T lymphocyte activation

OK that’s it for now!!! Feel free to share this article in social media.

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