What are the first and second signals in activation of a T C

What are the first and second signals in activation of a T Cell?

Solution

Activation of T-cell:

There are two signals that will fully activate the T-cells. These are described as follows:

A first signal,

It is antigen-specific,

It includes the interaction between TCR ( T cell receptor)and peptide-MHC(major histocompatibility complex) molecules on the membrane of antigen presenting cells (APC).

A second signal,

It is antigen nonspecific

It is provided by the interaction between co-stimulatory molecules expressed on the membrane of APC (antigen presenting cells) and the T cell.

It is also known as the co-stimulatory signal because it stimulates those T-cell in conjunction with antigens. let us see this a little more in detail: T - cell has CD -28 cells on it\'s surface. now, these T-cells binds with the resting APC with the help of T-cell receptor. now, if it does not recognise and binds with the antigen, it will remain non -responsive and will die. Whereas, If the APC process the antigen and present it on it\'s surface then CD-28 cells will bind with this antigen. note that here still from the other side it is already bound to the APC with the T-Cell receptor. now, these two bindings together only would result in the activation of the T-cell. so, therefore it is known as co-stimulatory signal.