Measurement of serum Interleukin 34 (IL-34) and correlation with severity and pruritus scores in client-owned dogs with atopic dermatitis

Background: Atopic dermatitis (AD) is a common inflammatory skin disease of dogs. Interleukin (IL)-34 is a monocyte/macrophage growth factor, produced mainly by keratinocytes, that has been implicated in several human inflammatory conditions including human AD. Hypothesis: Canine serum IL-34 concentrations are increased in dogs with AD and correlate with clinical lesion and pruritus scores. Animals: Forty seven client-owned dogs diagnosed with AD and 25 healthy, unaffected control dogs. Methods and materials: A commercially available IL-34 ELISA was optimized for the measurement of IL-34 in canine serum samples. Information regarding treatment, clinical lesion scores [Canine Atopic Dermatitis Extent and Severity Index, 4th iteration (CADESI-04)] and pruritus Visual Analog Score (pVAS) were recorded for each dog at the time of serum collection. Results: Dogs with AD had significantly increased serum IL-34 concentrations compared to controls. There was a significant positive correlation between IL-34 concentrations and CADESI-04 and pVAS scores. Concentrations of IL-34 remained increased in dogs with AD receiving steroids or the JAK1 inhibitor, oclacitinib, compared to unaffected control dogs. Conclusions and clinical importance: Serum IL-34 concentrations are increased in dogs with AD and are correlated with clinical severity and pruritus. IL-34 may be a suitable candidate therapeutic target for canine AD