Increased ratio of F ox P 3+ regulatory T cells/ CD 3+ T cells in skin lesions in drug‐induced hypersensitivity syndrome/drug rash with eosinophilia and systemic symptoms

Summary Background Drug‐induced hypersensitivity syndrome/drug rash with eosinophilia with systemic symptoms ( DIHS / DRESS ) is a severe drug eruption accompanied by multiorgan disorders. Several unique aspects of DIHS / DRESS , including herpesvirus reactivation, liver dysfunction and hypogammaglobulinaemia, have similarities to graft‐versus‐host disease ( GVHD ). Aim In this study, we focused on the dynamics of regulatory T cells ( T regs) infiltrating into the skin lesions of DIHS / DRESS and GVHD . Methods Skin biopsies were taken from patients with DIHS / DRESS , GVHD , or maculopapular drug eruption. Tregs were detected using immunostaining with anti‐ F ox P 3. Results The ratio of F ox P 3+ T cells to CD 3+ T cells was significantly higher in the skin lesions of patients with DIHS / DRESS than in those of patients with GVHD , and was positively correlated with the number of days from disease onset in the acute phase. Conclusions The dynamics of Tregs in skin lesions are different between DIHS / DRESS and GVHD , despite there being many similarities between these conditions.