Final answer:
Cytotoxic T cells destroy virus-infected or cancerous cells by recognizing pathogen epitopes presented on MHC I molecules, releasing perforin and granzymes to induce apoptosis.
Step-by-step explanation:
Cytotoxic T cells, also known as killer T cells, play a crucial role in the immune system by targeting and destroying cells that are infected with viruses or are cancerous. These cells, once activated, recognize and bind to pathogen-specific epitopes presented on the infected cells' surface with MHC I molecules. The cytotoxic T cell then releases perforin and granzymes, leading to the formation of pores in the target cell membrane and the induction of apoptosis. This process effectively kills the infected cell, limiting the spread of the virus and the risk of the infection worsening.
After the infection is under control, most cytotoxic T cells undergo apoptosis themselves, but some persist as memory cells. These memory cells are able to quickly proliferate and create new cytotoxic T cells if the same pathogen attacks again, providing a rapid and robust immune response. This ability to remember past infections is fundamental to the adaptive immune system's ability to prevent re-infection by the same pathogens.