The role of the T lymphocytes is to destroy body cells that have been infected by the pathogen. T lymphocytes recognise the antigens of the pathogen on the surface of the cell and induce apoptosis (programmed cell death).
T lymphocytes attach onto infected cells and release proteins. These proteins diffuse into the infected cells. This causes production of self-destructive enzymes, which cause cell death. The remains of the cell are then removed by phagocytosis.
T lymphocytes can identify the difference between antigens found on the body's own cells (self-antigens) and antigens belonging to the pathogen (non-self-antigens).
However if the immune system fails to recognise the difference between self and non-self-antigens it can result in T lymphocytes attacking the body's own cells. This can lead to autoimmune diseases.
Examples of autoimmune diseases include rheumatoid arthritis and type 1 diabetes.