Page 645 - Veterinary Immunology, 10th Edition

substance P, not only mediates pain and inflammation but also has
VetBooks.ir significant antibacterial activity. Other neuropeptides have similar

effects. As a result, appropriate nervous stimulation can promote
neuropeptide release and enhance local antibacterial activity. The

pain associated with acute inflammation may well reflect this local
resistance to infection. Some neuropeptides can promote Th17
activity by triggering monocyte production of IL-23.
Immune responses are also modulated by environmental factors.

Changes in day length (photoperiod) influences immune responses.
These effects can be complex, but in general reduced day length
appears to promote immune reactivity. The effect appears to be
mediated through the hormone melatonin. Circadian rhythms also

regulate some immune functions such as the activities of
hematopoietic stem cells and lymphocyte recruitment from the
blood. These appear to be a result of oscillations in chemokine
levels and the expression of adhesion molecules on vascular

endothelial cells.
Finally, the innate immune system can influence nervous
function. For example, cytokines such as IL-1, IL-6, and TNF-α as
well as other inflammatory mediators induce “sickness behavior,”

including fever, fatigue, depressed activity, and excessive sleep. All
these are closely associated with the systemic response to infectious
agents and chronic inflammation (Chapter 7).

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