Page 595 - Veterinary Immunology, 10th Edition

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FIG. 19.11 A schematic diagram showing the many functions of
NK cells. ADCC, antibody-dependent cellular cytotoxicity; GVH,
graft-versus-host.

NK cells can destroy some cultured tumor cells, and there is a
positive correlation between this activity in vitro and resistance to
tumor cells in vivo. Experimentally, it is possible to increase
resistance to tumor growth in vivo by passive transfer of NK cells

from a resistant animal. NK cells destroy human leukemia,
myeloma, and some sarcoma and carcinoma cells in vitro, and this
activity is enhanced by IFN-γ. NK cells can also invade small

primary mouse tumors. Some carcinogenic agents and low doses of
radiation inhibit NK activity. Stressors such as surgery may also
depress NK activity and so promote tumor growth. NK cells also
play an important role in the maintenance of pregnancy (Chapter
34).

Memory NK Cells

NK cells increase in numbers in response to stimulation and are
removed once invaders have been eliminated. Some may, however,
develop a “memory” and mount a form of secondary response to

some antigens. For example, NK cells bearing a KIR specific for
cytomegalovirus can expand their numbers in response to viral
antigen. Thereafter these NK “memory” cells persist in both
lymphoid and nonlymphoid tissues for several months. These self-

renewing memory cells are reactivated on re-exposure to the viral
antigen. Adoptive transfer of these reactivated NK cells leads to a
rapid expansion of their numbers and protective immunity to

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