Page 547 - Veterinary Immunology, 10th Edition

VetBooks.ir After reading this chapter, you will be able to:

• Define apoptosis, death receptor, caspase, perforin, granzyme, CD95.
• Describe the processing of endogenous antigens.
• Describe and compare the two major pathways of apoptosis.

• Explain how T cell–mediated immune responses eliminate abnormal cells and
intracellular organisms.
• Describe how the elimination of abnormal cells involves the forced apoptosis of

target cells by cytotoxic T cells.
• Describe how cytotoxic T cells kill their targets.
• Describe the characteristic features of cytotoxic T cells.

• List the signals required to activate a cytotoxic T cell.
• Discuss how some bacteria and parasites may evade destruction by living within

the endosomes or cytosol of phagocytic cells.
• Explain how the elimination of intracellular organisms is mediated by activation
of macrophages.
• Discuss the role of M2 macrophages in wound healing and recovery from

infection.
• List other methods by which the immune system can eliminate unwanted cells.

• Describe how effector memory T cells are generated.

Antibodies bind to invading organisms in blood or tissue fluids,
hastening their destruction. However, not all foreign organisms are
found outside cells. All viruses and some bacteria grow inside cells
at sites inaccessible to antibodies. Antibodies are therefore of

limited use in defending the body against such invaders. Viruses
and other intracellular organisms must be eliminated by other
mechanisms. For this, the body uses two different cell-mediated

processes. Either infected cells are killed rapidly by T cells so that
the invader has no time to grow, or alternatively, infected
macrophages develop the ability to destroy the intracellular
organisms. In general, organisms such as viruses that enter the cell
cytosol or nucleus are killed by cell destruction (cytotoxicity),

whereas organisms such as bacteria or parasites that reside within
endosomes are destroyed by macrophage activation. T cells mediate
both processes. The antigens that trigger these immune responses

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