Page 41 - Veterinary Immunology, 10th Edition

minor structural abnormalities may be recognized as foreign by the
VetBooks.ir immune system and destroyed, though they are otherwise

apparently healthy. These abnormal cells include aged cells, virus-
infected cells, and some cancer cells. The immune response to

foreign cells as shown by graft rejection is mediated by cytotoxic T
cells that identify and destroy the “abnormal” cells.
If a piece of skin is transplanted from one dog to a second,
unrelated dog, it will survive for about 10 days. The grafted skin

will initially appear to be healthy, and blood vessels will develop
between the graft and its host. By 1 week, however, these new
blood vessels will begin to degenerate, the blood supply to the graft
will be cut off, and the graft will eventually die and be shed (Fig.

1.8). If the experiment is repeated and a second graft is taken from
the original donor and placed on the same recipient, then the
second graft will survive for no more than a day or two before
being rejected. Thus the rejection of a first graft is relatively weak

and slow and analogous to the primary antibody response, whereas
a second graft stimulates very rapid and powerful rejection similar
in many ways to the secondary antibody response. Graft rejection,
like antibody formation, is a specific adaptive immune response in

that a rapid secondary reaction occurs only if the second graft is
from the same donor as the first. Like antibody formation, the graft
rejection process also involves the generation of long-lived memory
cells, since a second graft may be rapidly rejected many months or

years after loss of the first.

FIG. 1.8 The time course of the rejection of a foreign skin graft.

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