Page 891 - Veterinary Immunology, 10th Edition

VetBooks.ir Evasion of the Immune Response by

Viruses

As discussed earlier, during the millions of years they have
coexisted with animals, viruses have evolved numerous methods of
evading host immune responses (Fig. 27.7).

FIG. 27.7 Some of the ways by which viruses evade immune
destruction.

RNA viruses have a very small genome with little room to spare
for genes dedicated to suppressing immunity. As a result, RNA
viruses tend to rely on antigenic variation as their principal
mechanism of immune evasion. On the other hand, DNA viruses

have a larger genome and can afford to devote many different
genes to immune evasion. In large DNA viruses such as the
poxviruses and herpesviruses, as much as 50% of the total genome
may be devoted to immunoregulatory genes.

Negative Cytokine Regulation

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