This animation describes how helper T cells are activated and proliferate in response to an antigen.

Helper T cells work to regulate and coordinate the immune system. Each helper T cell is designed to recognize a specific antigen (a protein fragment taken from an invading pathogen, such as a virus or bacterium). The animation illustrates what happens when a helper T cell recognizes its antigen. The T cell triggers a series of events that cause it to proliferate into thousands of clones. These many identical T cells can stimulate other immune system cells to help destroy the pathogen.

Depending on students’ background, it may be helpful to pause the animation at various points to discuss different components or steps of the molecular pathway shown.