Page 642 - Veterinary Immunology, 10th Edition

structures. A dominance hierarchy regulates many mammalian
VetBooks.ir populations. Depending on the way the hierarchy is established,

some members may be very highly stressed. Animals of high rank
will be stressed if it requires constant fighting to maintain

dominance. This occurs, for example, in wild dogs, lemurs, and
mongooses. In hierarchies in which dominant members intimidate
through psychological intimidation, such as in mice, rats, and many
monkeys, low ranking individuals may be stressed and

immunosuppressed. If new individuals are introduced into a
group, or a dominant animal loses its position, stresses occur as a
result of the reorganization. In pigs, it has been shown that there is
a relationship between social status and disease susceptibility. Thus

morbidity and mortality among pigs challenged with pseudorabies
virus were highest among subordinate animals. Dominant pigs had
lymphocytes that were more responsive to virus antigens. This of
course makes sense from an evolutionary point of view in that the

least reproductively fit animals were more likely to die of disease,
but it is difficult to separate cause and effect in this phenomenon.
Were subordinate animals immunosuppressed because they were
under stress as a result of their lowly status? Alternatively, could it

be that those animals with a highly effective immune system were
healthier and thus better able to reach high social status within the
population? Certainly high levels of social stress are found in
confined, crowded animal populations. Social subordination in

rhesus monkeys results in changes in gene expression that are
biased toward inflammation including genes associated with
lymphocyte proliferation, innate immunity, and cytokine
responsiveness. Thus in stressed subordinate monkeys, TLR4

signaling predominantly used the MyD88- NF-κB pathway, while
in dominant monkeys they used the TRIF-IFN pathway (Chapter 2).
When the behavior of pigs is examined, they can be divided into
two groups: aggressive animals that tend to fight other animals and

then may flee rapidly, and passive animals that tend to cope with
stress by withdrawing gradually from stressful situations.
Aggressive pigs had higher in vitro and in vivo cell-mediated
immune responses but lower humoral responses than passive
animals. This suggests that there were differences in their relative

Th1 and Th2 responses. However, when these animals were

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