Severe atopic dermatitis is characterized by selective expansion of circulating T_H2/T_C2 and T_H22/T_C22, but not T_H17/T_C17, cells within the skin-homing T-cell population

Background Past studies of blood T-cell phenotyping in patients with atopic dermatitis (AD) have provided controversial results and were mostly performed before the identification of T_H9, T_H17, and T_H22 T-cell populations in human subjects. Objective We sought to quantify T_H1, T_H2, T_H9, T_H17, and T_H22 T-cell populations and corresponding CD8⁺ T-cell subsets in both cutaneous lymphocyte antigen (CLA)-positive and CLA^- T-cell subsets in patients with AD and control subjects. Methods We studied 42 adults with severe AD (mean SCORAD score, 65) and 25 healthy subjects using an 11-color flow cytometric antibody panel. Frequencies of IFN-γ-, IL-22-, IL-13-, IL-17-, and IL-9-producing CD4⁺ and CD8⁺ T cells were compared in CLA^- and CLA⁺ populations. Results We measured increased T_H2/T_C2/IL-13⁺ and T_H22/T_C22/IL-22⁺ populations (P <.1) in patients with severe AD versus control subjects, with significant differences in CLA⁺ T-cell numbers (P <.01). A significantly lower frequency of CLA⁺ IFN-γ-producing cells was observed in patients with AD, with no significant differences in CLA^- T-cell numbers. The CLA⁺ T_H1/T_H2 and T_C1/T_C2 ratio was highly imbalanced in patients with AD (10 vs 3 [P =.005] and 19 vs 7 [P <.001], respectively). Positive correlations were found between frequencies of IL-13- and IL-22-producing CD4⁺ and CD8⁺ T cells (r = 0.5 and 0.8, respectively; P <.0001), and frequencies of IL-13-producing CLA⁺ cells were also correlated with IgE levels and SCORAD scores. Patients with AD with skin infections had higher CD4⁺ IL-22⁺ and IL-17⁺ cell frequencies, which were highly significant among CLA^- cells (IL-22: 3.7 vs 1.7 [P <.001] and IL-17: 1.7 vs 0.6 [P <.001]), with less significant effects among CLA⁺ T cells (IL-22: 11 vs 7.5, P =.04). Conclusions Severe AD is accompanied by expansion of skin-homing T_H2/T_C2 and T_H22/T_C22 subsets with lower T_H1/T_C1 frequencies. These data create a critical basis for studying alterations in immune activation in adults and pediatric patients with AD.