Final answer:
The protein released by cytotoxic T cells to perforate a target cell's plasma membrane, allowing enzymes to enter and induce apoptosis, is called perforin.
Step-by-step explanation:
The protein released by cytotoxic T (TC) cells that perforates a target cell's plasma membrane is perforin. TC cells encounter an infected cell displaying an abnormal peptide bound to MHC class I molecules. Upon recognition, they release perforin and granzymes. Perforin forms pores in the plasma membrane, through which granzymes enter. Inside, these proteolytic enzymes trigger apoptosis, a form of programmed cell death, effectively fragmenting the target cell's DNA and enabling the immune system to eliminate infected or abnormal cells safely.