Skin-associated lymphocytes in the peripheral blood of patients with atopic dermatitis:: Signs of subset expansion and stimulation

Background: Skin-associated T cells are defined by the cutaneous lymphocyte-associated antigen (CLA), In atopic dermatitis (AD), CLA(+) T cells harbor allergen-reactive memory cells, spontaneously secrete T,, cytokines, and display signs of increased in vivo activation, thus relating the subset to the central disease pathomechanisms. Objectives: It is not known whether the proportion of circulating CLA(+) T cells might be expanded in AD. We were therefore prompted to compare the peripheral blood lymphocyte subpopulations of patients with AD with those of control subjects. Methods: We used 3-color flow cytometry to investigate age-matched peripheral blood samples of pediatric and young adult patients with mild (n = 21) or severe (n = 15) AD, patients with allergic/atopic diseases not involving the skin (n = 9), and healthy control subjects (n = 14), Results: We found no differences among the study groups with respect to the general proportions of T cells, CD4(+) T cells, CD8(+) T cells, B cells, NK cells, CD103(+) T cells, and CD25(+) T cells among total circulating lymphocytes. However, there were slightly more CD4(+) memory cells and clearly more HLA-DR+ T cells in patients with severe AD. Most remarkably, patients with severe AD had a significantly expanded proportion of CLA+ T cells (P = .024) and CLA(+)/CD4(+) T cells (P = .006) but similar proportions of CLA(+)/CD8(+) T cells compared with control subjects. Patients with severe AD also had distinctly more HLA-DR+/CLA(+) T cells than control subjects (P = .005). Similar alterations were seen in patients with mild AD, but these mere not statistically significant. After correction for age, all differences were significant only in probands less than 10 years of age. Conclusion: Circulating skin-associated T cells (CLA(+)) show signs of subset expansion and enhanced activation in patients with AD. These alterations, compared with control values, affect CD4(+) memory T cells in particular and are prominent only in children less than 10 years of age.