Granzymes are exogenous serine proteases that are released by cytoplasmic granules within cytotoxic T cells and natural killer cells. Their purpose is to induce apoptosis within virus-infected cells, thus destroying them.

Cytotoxic T cells and natural killer cells release a protein called perforin which attacks the target cells. Perforin creates pores within the cells, through which the granzymes can enter, inducing apoptosis.

Granzyme secretion can be detected and measured using the ELISPOT and ELISA techniques.

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