Th17/Tc17 infiltration and associated cytokine gene expression in elicitation phase of allergic contact dermatitis

Background Allergic contact dermatitis (ACD) is a typical delayed-type hypersensitivity to sensitizing haptens mediated by T cells. Th1/Tc1 cells are currently considered to be the primary effectors in ACD. There is little information concerning the role played in ACD in humans by Th17/Tc17 cells, a recently defined subpopulation of effector T cells. Objectives In the present report we attempted to characterize Th17/Tc17 cells in the infiltrates of the skin in the elicitation phase of ACD. Methods Th17 as well as Th1/Th2 cytokine gene expression was examined by semiquantitative real-time polymerase chain reaction in paired samples of positive patch test biopsies and normal skin from 11 patients allergic to nine different allergens. The in situ characterization of interleukin (IL)-17-producing cells was carried out using anti-RORC and anti-T-cell subset antibodies by double immunofluorescence. Results Compared with normal paired skin samples, gene expression of transcription factor for human Th17 cells, RORC, and Th17-related cytokines IL-17A, IL-17F and IL-23 was significantly increased in positive patch test biopsies. The mRNA for interferon-γ and IL-4 was also increased. In the dermal infiltrates, about 20% of the infiltrating cells were IL-17-producing cells as they expressed RORC, and such RORC-expressing cells were detected in both CD4+ (∼30%) and CD8+ (∼20%) subsets. Conclusions This is the first demonstration of Th17/Tc17 cells in the elicitation phase of human ACD, showing that they are a regular participant in the immunopathology of this common allergic reaction regardless of the nature of the triggering allergen.