To defend against pathogens that live in the cytoplasm (mostly viruses) & certain tumor cells.
How does the Tc cell recognize a normal cell with a hidden enemy inside?
T cell receptors bind to an antigen fragment & a self molecule.
(MHC class I is the self molecule. It collects peptides derived from proteins synthesized in the cytosol. Any viral protein made by the cell is also displayed and helps in recognition.)
What activates the T cell?
IL-2 produced by Helper T cell.
Is there an other way to activate the Tc cell?
Yes! Through potent antigen presenting cells.
It happens in case of certain viral infections only.
How does it kill the target cell?
Tc cells come in close contact with the target cell, and release preformed cytoxins from their granules.
(It’s like coming close & stabbing someone).
Cytotoxins are released tightly focused at the site of contact without killing any uninfected cells nearby.
(They are very lethal so they have to be very precise in killing.)
Perforins deliver granzymes
(Perforins are like an injection for delivering medicine).
Granzymes induce apoptosis.
(They convince the cell that it is infected & it must die).
Granulysins creates holes in the target cell. It causes osmotic damage to the cell.
(Something like stabbing & letting them bleed to death).
It can also induce apoptosis through Fas-Fas ligand interaction.
But it is not used for killing infected cells, it is used for disposing unwanted lymphocytes.
(That’s why I haven’t included it in the diagram.)
I’ll be doing the detailed mechanisms a bit later. This is just a very short summary.
Hope you are having an amazing month so far!