The process begins when an antigen-presenting cell (APC) such as a _dendritic cell_ or _macrophage_ processes an antigen and presents it on its surface using _MHC (Major Histocompatibility Complex)_ molecules. This antigen-MHC complex is recognized by T cells, specifically _helper T cells (CD4+)_ and _cytotoxic T cells (CD8+)_. The helper T cells then secrete cytokines that further activate cytotoxic T cells and other immune cells to target and destroy infected cells.
