Page 560 - Veterinary Immunology, 10th Edition

Although the size of the central pore of the polyperforin permits
VetBooks.ir granzyme monomers and dimers to enter target cells, killing also

occurs at low perforin concentrations. It is believed that perforins
may also release granzymes from target cell endosomes.

FIG. 18.9 Perforins from human natural killer cells on the surface
of a rabbit erythrocyte target. The arrowheads point to incomplete
rings and double rings. (From Podack ER, Dennert G: Assembly of two types
of tubules with putative cytolytic function by cloned natural killer cells, Nature
301:442-445, 1983.)

Granzymes are serine proteases found in T cells, where they
account for about 90% of the total granule contents. Granzyme A is
most abundant and triggers apoptosis of target cells. It destroys
histones and releases a nuclear deoxyribonuclease. It is this enzyme

that causes the DNA damage. Granzyme B then enters the target
cell, either by injection through the central pore of the perforin
complex or by endocytosis. It activates pro-apoptotic bcl-2 proteins,

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