Plasmacytoid dendritic cells diminution in peripheral blood is prevalent in drug reaction with eosinophilia and systemic symptoms and may precede human herpesvirus 6 reactivation

Background: Plasmacytoid dendritic cells (pDCs) are implicated in the reactivation of human herpesvirus 6 (HHV-6) in drug reaction with eosinophilia and systemic symptoms (DRESS). Objectives: We aimed at identifying the alterations of circulating pDCs, basophils, and myeloid dendritic cells (mDCs) during the active stage of drug eruptions and the relationship between pDC alteration and HHV-6 reactivation in DRESS patients. Methods: Nine DRESS patients and twelve patients of other drug eruptions (ODE, including five cases of maculopapular eruptions (MPEs), five cases of Stevens–Johnson syndrome, and two cases of fixed drug eruption) were prospectively recruited. Blood samples were collected weekly for 2 consecutive weeks for flow cytometry of pDC, basophil, mDC, and detection of HHV-6 reactivation by serum anti-HHV-6 immunoglobulin G, or whole blood HHV-6 viral DNA by quantitative polymerase chain reaction. Results: The HHV-6 reactivation was exclusively seen in DRESS, and the pDC levels decreased in DRESS compared with ODE (P = 0.002) and (MPE, P = 0.021), with the timing of such decrease preceding HHV-6 reactivation. Conclusion: The decrease of pDC levels is significantly more common in DRESS patients and occurs before HHV-6 reactivation. The chronological sequence implies that the decrease of pDC may be crucial in the pathogenesis of viral reactivation.