CHAPTER 11 ATOPIC DISEASE 175
Additional research has demonstrated increased expression of Th 1 and Tregcytokines
in chronic disease.
Tregcells may be induced by ASIT to promote tolerance. Cytokines reported to be
pruritogenic or proinflammatory include IL-2, IL-4, IL-6, IL-13, and IL-31.
IL-31 and JAK/STAT
Reported increased levels of cytokine IL-31 in atopic skin; IL-31 can induce pruritus
in normal dogs.
Blocking of IL-31 (by neutralizing antibody) or its receptor on neurons (JAK1
inhibitor) can reduce the symptoms of atopic dermatitis.
The role of this cytokine in the development of hypersensitivity and inflammation
(versus strictly as a pruritogenic cytokine) remains to be determined.
Summary Based on Current Knowledge
Susceptible animals (barrier dysfunction/immune dysregulation) become sensitized
to environmental allergens.
Repeat allergen exposure (most importantly by percutaneous absorption and less so
by oral exposure) causes a hypersensitivity reaction, and results in the release of
mediators of inflammation that may include histamine, heparin, proteolytic enzymes,
leukotrienes, serotonin, cytokines, chemokines, and perhaps many others.Cumulative pruritogenic factors (insect, food, environmental allergens, bacterial
and yeast antigens) may lower the individual threshold (further barrier dysfunc-
tion/immune hyperreactivity), leading to persistent clinical symptoms in some
patients or intermittent clinical symptoms in others (allergic threshold principle),SIGNALMENT/HISTORY
Risk factors reported or proposed for the development of canine AD: exposure/lack
of exposure to environmental allergens (“hygiene hypothesis”), environmental pro-
teases (e.g., house dust mite antigens), and oxidative stress (e.g., tobacco smoke).Canine: true incidence unknown; estimated at 3–27% of the canine population; with
efficacy of newer parasiticides, AD may replace flea bite dermatitis as the most com-
mon allergic skin disease.Feline: unknown; generally believed to be lower than for dogs.
Canine: any breed, including mongrels; although it may not have a simple mode of
inheritance, it has been recognized more frequently in certain breeds or families.
Canine: Boston terriers, boxers, cairn terriers, cocker spaniels, dalmatians, English
bulldogs, English setters, French bulldogs, German shepherds, Irish setters, lhasa
apsos, miniature schnauzers, pugs, Sealyham terriers, Scottish terriers, West Highland
white terriers, wire-haired fox terriers, and golden retrievers.Canine: mean age at onset 1–3 years; range 3 months to 6 years; symptoms may be
mild initially but are usually progressive and clinically apparent by 3 years of age.