Question

The principal mechanism through which cytotoxic T cells act is by the calcium-dependent release of specialized lytic granules upon recognition of antigen on the surface of a target cell. These granules are modified lysosomes that contain at least two distinct classes of cytotoxic effector protein that are expressed selectively in cytotoxic T cells. Such proteins are stored in the lytic granules in an active form, but conditions within the granules prevent them from functioning until after their release. One of these cytotoxic proteins polymerizes to generate transmembrane pores in target cell membranes. What is it called?

a) Perforin
b) Opsonin
c) Immunophilin
d) Leukocidin
e) RTX toxin

Answer 1

Perforin is the cytotoxic protein that forms transmembrane pores in target cell membranes, enabling granzymes to enter and induce apoptosis.

Step-by-step explanation:

The cytotoxic protein that polymerizes to form transmembrane pores in target cell membranes is called perforin. Perforin is a key component of the defensive strategy employed by cytotoxic T cells, which are activated to fight against cells infected by intracellular pathogens.

The cytotoxic T cells recognize these infected cells through antigen presentation with MHC I molecules, and upon recognition, they release both perforin and another class of cytotoxic proteins known as granzymes. Perforin's role is to create pores in the membrane of the target cell, through which granzymes can enter, leading to apoptosis, the controlled destruction of the infected cells.