In the innate immune response, natural killer cells primarily target infections and tumors by using a type of molecule known as __________.

Natural killer cells attack infected or cancerous cells by releasing a protein called perforin, which punches holes in the target’s cell membrane. This creates pores that allow toxic enzymes called granzymes to enter the victim cell. Once inside, the granzymes trigger programmed cell death, or apoptosis. For example, when a virus‑infected cell is spotted, the NK cell releases perforin to open a hole, letting granzymes kill the cell quickly. This quick, antibody‑independent method is a hallmark of innate immunity.