- Cytokines, released by helper T cells and APCs, act as costimulators. Cytokines are protein hormones that influence cell growth. When a helper T cell becomes activated or an APC engulfs an antigen, the helper T cell or APC secretes a cytokine called interleukin.
- Helper T cells and APCs act as costimulators. Activated T cells or APCs that display antigens activate B cells or T cells when they temporarily bind to them.