T cells are specific. T cells recognize individual harmful particles which allows them to mount powerful neutralizing immune responses.

What does it mean that T cells are specific?

T cells can recognize whether a cell or particle belongs to the body and whether the cell is healthy or unhealthy. T cells can also recognize whether a macrophage has eaten something (like a bacteria) that might pose a threat to the health of the organism or whether it is not harmful. T cells make this decision by identifying the proteins (antigens) that each cell displays on their surface. T cells are specific because they are able to recognize the specific antigen, and mount an immune response that targets only that antigen.

The Importance of Specificity

The relevance of the specific T cells is that they only attack cells that present nonself antigens, as opposed to killing healthy cells. It also allows the immune cells to "share" this information with other cells and propagate a specific immune reaction:

1. 1 - Once activated, the T cell replicates to multiply the number of cells that have the correct binding site.
2. 2 - The activated Killer T cell will go on to only kill the precise type of cell in question.
3. 3 - Helper T cell will go on and activate more T cells that share the same binding site to propagate the reaction.
4. 4 - Both kinds of T cells will create some cloned copies that will remain in the body, keeping some immune cells with that antigen-binding site at the ready in case the germ ever appears again.

How Specificity Works for T cells

We talk a lot about specificity, but you might be wondering how it all works.  The mechanisms behind the specific immune response involve:

• STEP 1 - T Cells must bind to the target cell: the MHC
• STEP 2 – The T cells must distinguish healthy from unhealthy cells: distinguishing self from nonself antigen

Binding or attachment between proteins is the basis for specificity

The binding referred to in this section happens when two cells (or more) have proteins on their surface that fit each other kind of like a lock and a key, so that the two cells attach briefly to each other. We refer to the proteins on both cells as “binding sites” or “receptor sites.”

T cells have special spots on their membrane where the binding occurds: the T cell receptor site (TCR). The TCR actually contains two sites: one that binds particular spots on a cell’s surface, the Major Histocompatability Complex (step 1 - The MHC), and a second receptor site that binds with the antigen displayed (step 2 - distinguishing self from nonself antigen ). Each T cell has many TCR binding sites. But each T cell only has one kind of antigen receptors, so it can only “fit” only one particular antigen, like a lock and key. This makes them specific, allowing T cells to know which particular pathogens like bacteria and viruses is in your body.

The interaction between molecules involved is very complex and depends on their three-dimensional structure and their electrical charge. Protein-mediated binding happens all throughout the body in many different ways and is vital to most biological processes.