Recently, it was suggested that CD4+CD25+FoxP3+ Tregs (Regulatory T-cells) exist in canine skin, although their numbers were not significantly different between healthy and atopic dogs. In this study, we investigated whether Treg frequencies correlate with the clinical features of canine atopic dermatitis (cAD). The goal of this study was to compare and analyse the numbers of the circulating Tregs in atopic and healthy dogs. In the peripheral blood mononuclear cells (PBMC) of healthy dogs, Tregs defined as CD4+CD25+FoxP3+ Tregs in the peripheral blood ranged from 0.3% to 1.5%. By contrast, in atopic dogs, the same population ranged from 0.7% to 8.8%. The percentage of CD4+CD25+FoxP3+ Tregs in gated CD4+ T-cells was significantly higher in the peripheral blood of dogs with atopic dermatitis (n = 9) than in the healthy controls (n = 8). The difference in the Treg levels (CD4+CD25+FoxP3+) (P = 0.012) between the atopic and the healthy groups was statistically significant. The circulating T-cells (phenotype CD4+CD25+FoxP3+ and CD4+FoxP3+) were increased significantly in the atopic dogs. The proportion of CD4+CD25+FoxP3+ Tregs of the atopic dogs decreased with advancing age. These findings suggest that changes in the Tregs may mediate the pathogenesis of CAD.
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