Page 1118 - Veterinary Immunology, 10th Edition

VetBooks.ir Renal Allografts

Renal allograft rejection is of major clinical importance in humans
and has been widely studied in animals. It therefore serves as a

good example of the allograft response. Rejection may occur at any
time after transplantation. In humans, in whom a great deal of
experience with transplantation has been gained, four distinct
clinical rejection syndromes are recognized. Hyperacute rejection
occurs within 48 hours after grafting. Rejection occurring up to 7

days after grafting is called accelerated rejection. Rejection after 7
days is called acute rejection. Chronic rejection develops several
months or years after grafting. It is unclear whether a similar

classification is useful in animals.
When kidneys are allografted, the blood supply to the
transplanted kidney is established at the time of transplantation.
The graft and host cells come into contact almost immediately. In an
unsensitized host, a primary immune response is mounted, and

renal allografts are only rejected after at least 10 days and possibly
much longer. In sensitized animals in which the immune system is
already primed, hyperacute rejection occurs, and the graft is

destroyed within days or even hours without ever becoming
functional. Acute rejection should be suspected when the recipient
shows a rapidly rising blood creatinine associated with an enlarged,
painful kidney accompanied by signs of depression, anorexia,
vomiting, proteinuria, hematuria, and ultrasonography showing an

enlarged, hypoechoic kidney. In contrast, chronic rejection should
be suspected if the creatinine and urea levels rise gradually, and
this is associated with proteinuria, microscopic hematuria, and a

small, hyperechoic kidney. This is also associated with a slow loss
of renal function and tends to be related to interstitial fibrosis and
proliferation of vascular endothelium. Renal biopsy is necessary to
confirm rejection. Interestingly, a significant number of feline renal
allograft recipients may also develop retroperitoneal fibrosis that

results in ureteral obstruction.

Pathogenesis of Allograft Rejection

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