A natural killer cell empties its granules onto an infected cell. Which molecule then digests proteins inside that cell to trigger apoptosis?

1. Natural killer cells kill by inducing apoptosis, that is, programmed cell death, in cells infected with intracellular pathogens. 2. One route uses the fas ligand on the killer cell, which binds the fas molecule on the infected cell and sends it apoptotic signals. 3. The other route empties the granules of the natural killer cell onto the target. 4. A perforin is a protein that forms pores in the membrane of the infected cell. 5. A granzyme is a protein-digesting enzyme that enters the cell through those perforin pores and triggers apoptosis inside it. 6. Perforin only opens the way in, so it is the trap for anyone who stops at the pore. 7. Fas ligand kills without using granules at all, and interferon is an antiviral protein secreted by virally infected cells. _Source: OpenStax Anatomy and Physiology (CC BY 4.0), Ch 21 "The Lymphatic and Immune System", section 21.2 Barrier Defenses and the Innate Immune Response_