Page 587 - Veterinary Immunology, 10th Edition

spleen to 15% of the lymphocytes in human blood. Their
VetBooks.ir characteristic cell surface phenotype is CD3 , CD56 , and NKp46 .
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Target Cell Recognition

NK cells do not make the enormous diversity of antigen receptors

employed by T and B cells. Instead, they use two types of receptors
to distinguish normal from abnormal cells. One type monitors the
expression of MHC class I antigens by cells; the other detects

“stress” molecules on unhealthy cells such as tumor or infected
cells.
NK cells thus recognize abnormal cells using two different
strategies. One is a “missing-self” strategy by which NK receptors
bind MHC class I molecules expressed on healthy cells, and as a

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result prevent NK cell killing of normal MHC class I cells (Fig.
19.6). If, however, a cell fails to express MHC class I, then inhibitory
signals are not generated, and it will be killed. This occurs, for

example, when a virus suppresses cellular MHC class I expression
to avoid destruction by cytotoxic T cells. Likewise, tumor cells that
fail to express MHC class I are also killed by NK cells.

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