An example of a cell-mediated immune response targeting virus-infected cells.

1. A dendritic cell engulfs a virus-infected cell. Digested fragments of the virus bind to MHC markers, and the complexes become displayed at the dendritic cell’s surface. The dendritic cell, now an antigen-presenting cell, migrates to a lymph node.Receptors on a naive cytotoxic T cell bind to the antigen–MHC complexes on the surface of the dendritic cell. The interaction activates the cytotoxic T cell.Receptors on a naive helper T cell bind to antigen–MHC complexes on the dendritic cell. The interaction activates the helper T cell, which then begins to divide.
2. A large population of descendant cells forms. Each cell has T cell receptors that recognize the same antigen. The cells differentiate into effector and memory cells.
3. The effector helper T cells begin to secrete cytokines.
4. The activated cytotoxic T cell recognizes these cytokines as a signal to divide.
5. A large population of descendant cells forms. Each cell bears T cell receptors that recognize the same antigen. The cells differentiate into effector and memory cytotoxic T cells.
6. The new effector cytotoxic T cells circulate throughout the body. They recognize and kill any body cell that displays the viral antigen–MHC complexes on its surface.