ABSTRACT. In this study, percentages of CCR4 + cells in peripheral CD4 + T-lymphocytes were examined with flow cytometry in 46 healthy beagles between 3 months and 7 years of age. The percentage of CCR4 + cells varied from 9.9% to 33.5%. The mean percentage was significantly lower in the group with ages of less than 1 year than those with ages equal to or more than 1 year (p<0.05), suggesting that maturation might increase the CCR4 + T-lymphocyte subset. No influence of aging on the percentages was detected among the groups with ages equal to or more than 1 year. The findings are useful for establishing a reference value for the percentage of peripheral CCR4 + CD4 + lymphocytes in dogs. KEY WORDS: canine, CCR4, lymphocyte.J. Vet. Med. Sci. 70(9): 989-992, 2008 Leukocytes express various types of chemokine receptors and show specific trafficking via interaction between those receptors and chemokines produced at inflammatory sites [18]. Specific expression profiles of chemokine receptors have been used to classify specific cell types, for instance, two different subsets of helper T-lymphocytes:Th1 and Th2 cells [1]. Among the chemokine receptors, it has been shown that Th1 cells selectively express CXC chemokine receptor (CXCR) 3 [13] and CC chemokine receptor (CCR) 5 [5], whereas Th2 cells express CCR3 [14] and CCR4 [3]. In human atopic dermatitis (AD), it was found that the frequency of CCR4 + cells among CD4 + T-lymphocytes increases in the peripheral blood [12] and lesional skin [11]. Additionally, the plasma concentration of CC chemokine ligand (CCL) 17, a ligand of CCR4, was reported to increase in human AD and correlates with disease severity [4]. These results suggest that the interaction between CCR4 and CCL17 plays an essential role in the immunopathogenesis of AD in humans. Similarly, in canine AD, expression of CCL17 [6] and CCR4 mRNAs [8] was detected in conjunction with the expression of inflammatory cytokines including IL-1β, IFN-γ, and TNF-α in lesional skin [6], and the number of CCR4 + cells also increased in peripheral CD4 + Tlymphocytes [7]. A recent study in dogs demonstrated that keratinocytes were the major CCL17-producing cells in lesional skin of dogs with canine AD [9]. These studies indicated that CCR4-CCL17 interactions might play important roles in canine AD, similar to those in human AD.In humans, it was reported that CCR4 was specifically expressed on peripheral CD4 + T-lymphocytes from patients with AD but not from patients with psoriasis vulgaris [16]. Moreover, the percentages of CCR4 + cells in peripheral CD4 + T-lymphocytes were reported to increase in correlation with disease severity and decreased with improvement by topical corticosteroid therapy [16]. CCR4 was preferentially expressed on peripheral CD4 + T-lymphocytes in dogs with canine AD compared with those in healthy dogs [7]. These indicated that CCR4 expression on CD4 + T-lymphocytes might be a useful marker to identify atopic diseases, monitor their disease severity, and evaluate effects of treatment in dogs as wel...