Biology, Eighth Edition (Raven)

Chapter 51: The Immune System

Cytotoxic T-Cell Activity against Target Cells

Why do target cells trigger their own destruction? One of the functions of T-cells in the immune system is to attack and destroy infected cells. Target cells are cells that have been attacked by a virus. The target cells present molecular information on their membranes that allow the cytotoxic T cells to identify and destroy them. Target cells have been taken over by a virus and do not have a good chance of surviving for long in any event. By triggering their own death they are reducing the chance that other cells nearby will become infected.

View the animation below, then complete the quiz to test your knowledge of the concept.


1.	Cytotoxic T cells produce

		A)	class II MHCs
		B)	self proteins
		C)	antibodies, which make holes in cell membrane of infected cells
		D)	perforin, which makes holes in cell membrane of infected cells

2.	Infected cells

		A)	display peptide fragments of degraded viral proteins on their cell surface
		B)	have class II MHC antigens on their cell surface
		C)	are not affected by T cells
		D)	lyse T cells

3.	Cytotoxic T cells recognize

		A)	receptors on B cells
		B)	fragments of self proteins of infected cells
		C)	viral antigens and class I MHC
		D)	viral antigens and class II MHC
		E)	all of the above

4.	Cytotoxic T cells produce cytotoxins which cause apoptosis of infected cells.

		A)	True
		B)	False

5.	Self proteins of infected cells are not recognized by cytotoxic T cells.

		A)	True
		B)	False