Evaluation of the cutaneous expression of IL-17, IL-22, IL-31, and their receptors in canine atopic dermatitis.

Interleukins (IL)-17, IL-22, and IL-31 play roles in human atopic dermatitis (AD), but scant information is available on canine AD. Histopathological assessment for interleukin expression is a challenge due to a lack of canine specific antibodies. To evaluate the mRNA and protein expression of IL-17 and IL-22, and mRNA expression of IL-31 and their receptors in the skin of healthy and atopic dogs, seventeen atopic (10 with and 7 without an active infection) and 13 healthy privately owned dogs were sampled. RNAscope® In situ hybridization (ISH) for IL-17, IL-22, IL-31, and their receptors was performed on archived canine skin samples. Simultaneously, indirect immunofluorescence (IIF) was performed for IL-17 and IL-22. RNAscope® ISH probes were validated by RT-PCR and RNAscope® ISH on cytospin preparations of peripheral blood mononuclear cells from atopic dogs. IL-17, IL-22, IL-31, and their receptors were successfully detected by RNAscope® ISH and by IIF (IL-17 and IL-22) in both atopic and healthy canine skin. There was no significant difference in the expression of interleukins and their receptors between healthy and atopic skin with or without active infection. Data from both methodologies were similar. The role and the relationship among those proteins in atopic skin is unclear from this study results. Data from IIF and ISH were overlapping and support each other. Fresh skin samples taken at different times during the development of atopic dermatitis might better assess the role that interleukins and their receptors play in AD.