T lymphocytes, abbreviated as T cells, also known as thymus-dependent lymphocytes, are the main components of lymphocytes, which have various biological functions, such as direct killing of target cells, assisting or inhibiting antibody production by B cells, responding to specific antigens and promoting mitogens, and producing cytokines, etc. They are the fighters in the body against disease infection and tumor formation. There are two main types of effect formation in cellular immunity: target cell-specific binding, destruction of target cell membranes, and direct killing of target cells; the other is the release of lymphokines, which ultimately expands and enhances the immune effect. t lymphocytes account for about 65%-75% of the total number of lymphocytes in peripheral blood and up to 95% or more in the thoracic duct. t lymphocytes can be divided into many types according to their function and surface markers. Cytotoxic T cells destroy infected cells, and these cells function like a killer or cytotoxin because they can kill target cells that produce a specific anti-inflammatory response. The main surface marker of cytotoxic T cells is CD8, and this is also known as a killer T cell.