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What is Perforin - and explain in detail?
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.