Granzyme
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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. Scientist used to think that Perforin creates pores within the cells, through which the granzymes can enter, inducing apoptosis. However, new evidences indicate that GrB complex (GrB, perforin, and another protein (glycopectin?)) can enter a cell through the mano-6-phosphate receptor (or another receptor currently found in tumor cell) and is enclosed in a vesicle (a sac). Perforin then allows GrB to pass through the vesicle surface and into the cell, causing apoptosis by various pathways. They do so by cleaving caspases, (especially caspace-3) which in turn activate caspase activated DNase. This enzyme degrades DNA, thus inducing apoptotic cascades. Also, GrB cleaves the protein Bid, which recruits the protein Box and Bak to change the membrane permeability of the mitochondria, causing the release of Cytochrome C (which is one of the parts needed to form Caspace-9), Smac/Diablo/Omi (which suppresses the IAP), among other proteins. As well, GrB is shown to cleave many of the chemicals responsible for apoptosis without the aid of caspace, as proven by experiments on caspace KO mice CTL cells incubated with other cells.
Granzyme secretion can be detected and measured using the Western Blot, ELISPOT and ELISA techniques. abc-sequence
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