1. it is a self-marker; it is made of proteins; if a cell gets infected, the cell will present pieces of the pathogen on its MHC proteins; cytoxic t cells are normall inactive but will recognize and bind to the MHC and is now activated- it will kill the cell and move on

2. When infected by a virus, a cell will display on its surface portions of the virus, bound to their MHC proteins.

· These antigen/MHC complexes act like flags or signals to cytotoxic T-cells.

· Inactive cytotoxic T-cells recognize these antigen/MHC complexes and bind to them.

· This binding then activates the cytotoxic T-cell.

· Active cytotoxic T-cells start dividing – a portion of the new cells are stored, inactive, as memory T-cells.

The rest of the new cytotoxic T-cells patrol the body, and recognize other virus-infected cells displaying the same antigen/MHC complex. These cells are killed by the cytotoxic T-cells. The cytotoxic T-cells then move on to other infected cells, to destroy them too.