Treatment-Associated Differences in Serum Cytokine Profiles in Canine Atopic Dermatitis: A Cross-Sectional Study

Systemic immunomodulatory treatments are widely used in canine atopic dermatitis (cAD), but treatment-associated differences in circulating cytokine profiles remain unclear. This cross-sectional study compared serum cytokine concentrations in 143 dogs: Healthy (n = 28), Untreated AD (n = 27), Prednisolone (n = 23), Oclacitinib (n = 29), Lokivetmab (n = 19), and Cyclosporine (n = 17). Serum concentrations of IFN-γ, IL-10, IL-13, IL-31, and TGF-β1 were quantified using enzyme-linked immunosorbent assays. pVAS and CADESI-04 were compared among the five cAD groups. All five cytokines differed significantly among the six groups. The Prednisolone group had lower pVAS scores than the Untreated AD group (p = 0.002) and the Cyclosporine group (p = 0.001), despite having the highest median serum IL-31 concentration (163.9 pg/mL), which was significantly higher than that in each of the other groups (p ≤ 0.003). The Prednisolone group showed lower IL-13 concentrations than the Healthy and Untreated AD groups (both p = 0.001). IFN-γ concentrations were lower in the Oclacitinib, Lokivetmab, and Cyclosporine groups than in the Healthy group (p ≤ 0.002). Serum cytokine profiles differed among groups defined by treatment status; however, these cross-sectional differences cannot be interpreted as direct treatment effects. The discordance between pVAS and serum IL-31 in the Prednisolone group indicates that circulating cytokine concentrations may not consistently parallel concurrent clinical severity and should be interpreted as a hypothesis-generating observation rather than an established biological relationship. Longitudinal studies are needed to clarify whether these profiles reflect treatment exposure, underlying disease heterogeneity, or both.