Page 898 - Veterinary Immunology, 10th Edition

VetBooks.ir Adverse Consequences of Immunity

to Viruses

The immune response to viruses can, on occasion, be a
disadvantage. Indeed, there are many virus diseases in which
disease results from inappropriate or excessive immune responses.
For example, bovine respiratory syncytial virus (RSV) induces a

type 2 response in infected cattle with production of IL-4 and
specific IgE antibodies in the lungs. This may result in a type I
hypersensitivity reaction since there is a direct correlation between
lung IgE levels and the severity of clinical disease.

The destruction of virus-infected cells by antibody is classified as
a type II hypersensitivity reaction (Chapter 31) and, although
normally beneficial, may exacerbate virus diseases. Thus viruses are
removed at the cost of cellular destruction. The severity and

significance of this destruction depend on how widespread the
infection becomes. In some diseases in which the virus causes little
cell destruction, most of the tissue damage may result from
immunological attack. A good example of this is seen in distemper

encephalitis, in which neurons are demyelinated as a result of an
antiviral immune response. Macrophages in these brain lesions
ingest immune-complexes and infected cells leading to the release
of oxidants and other toxic products. These toxic products damage

nearby cells, especially oligodendroglia, causing demyelination.
Type III (immune-complex) lesions (Chapter 32) are associated
with viral diseases, especially those in which viremia is prolonged.
For example, a membranoproliferative glomerulonephritis resulting

from the deposition of immune-complexes is a common
complication of equine infectious anemia, Aleutian disease of mink,
feline leukemia, chronic hog cholera, bovine virus diarrhea-mucosal
disease, canine adenovirus infections, and feline infectious

peritonitis. A generalized vasculitis due to deposition of immune-
complexes throughout the vascular system is seen in equine
infectious anemia, Aleutian disease of mink, malignant catarrhal
fever, and possibly equine viral arteritis.

In dogs infected with canine adenovirus-1 (infectious canine

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