Page 1005 - Veterinary Immunology, 10th Edition

and leukotrienes, some neuropeptides, and IL-31.
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FIG. 30.8 The major mediators associated with pruritus. The most
significant of these include histamine, thymic stromal lymphopoietin
(TSLP), and interleukin-31 (IL-31). These act on specialized nerve
receptors within the skin to induce itch.

In addition, epithelial cells can communicate directly with
cutaneous sensory neurons using TSLP. TSLP from keratinocytes
enables them to communicate directly with TSLP-sensitive neurons
through a pathway that does not require immune stimulation. It is

unclear what the relationship is between itch induced by TSLP and
itch induced through immune-cell neuronal communication and
histamine.
Since canine mast cells contain histamine, it has long been

assumed that histamine is the primary mediator of AD. It causes
vasodilatation, pain, and itching. However, histamine levels do not
correlate well with disease severity, and plasma histamine levels do
not differ significantly between normal and atopic dogs. Thus this

too suggests that AD is not simply a type I hypersensitivity
reaction.
The cytokine IL-31 causes severe pruritus in dogs and is elevated
in AD. Peripheral blood mononuclear cells from dogs exposed to

allergen (house dust mites) plus Staphylococcal enterotoxin B
produce high levels of IL-31. T cell mitogens also stimulate IL-31
production suggesting that T cells are the source of this cytokine.

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