How do T-cells work in the immune system?

T-cells play a key role in the adaptive immune system, coordinating various immune responses to protect the body against infections and diseases. 

There are two main categories of T-cells – cytotoxic T-cells, which are responsible for killing infected cells and destroying tumor cells, and helper T-cells, which help cytotoxic T-cells and B cells do their job more efficiently by sending signals and organizing effective immune responses against pathogenic intruders. 

T-cells possess unique T-cell receptors on their surface, which help them to identify specific antigens or protein fragments from pathogens or abnormal cells. On encountering antigen-presenting cells (APCs), cytotoxic T-cells get activated and work to kill the infected cells and destroy cancer cells. Meanwhile, activated helper T-cells send signals to other immune cells, instructing them as to what actions to take and coordinating an appropriate response.