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 d isplay signs of increased in vivo activation, thus relating the subset to t he 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 pe ripheral blood lymphocyte subpopulations of patients with AD with those of control subjects. Methods: We used 3-color flow cytometry to investigate age-matched peripher al blood samples of pediatric and young adult patients with mild (n = 21) o r 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, N K cells, CD103(+) T cells, and CD25(+) T cells among total circulating lymp hocytes. 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 a lso had distinctly more HLA-DR+/CLA(+) T cells than control subjects (P = . 005). Similar alterations were seen in patients with mild AD, but these mer e 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 subs et 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.