This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pathology
Perforin - 
Select and explain. 
A. Cytotoxic T cell, B. NK cell, C. Plasma cell, D. Monocyte
A: Cytotoxic T cell
Answer: A: Cytotoxic T cell 
Explanation: Cytotoxic T Lymphocyte-Mediated Apoptosis

Cytotoxic T lymphocytes (CTLs) recognize foreign antigens presented on the surface of infected host cells,
Upon activation, CTLs secrete perforin, a transmembrane pore-forming molecule, which promotes entry of the CTL granule serine proteases called granzymes.
Granzymes cleave proteins at aspartate residues and thus activate a variety of cellular caspases. In this way, the CTL kills target cells by directly inducing the effector phase of apoptosis.