Involvement of Plasmacytoid Dendritic Cells in the Immunological Response Against Orf Infection

Plasmacytoid dendritic cells (PDCs) are specialized dendritic cells with a significant role in antiviral resistance. 1,2lasmacytoid dendritic cells have never been studied in orf infection.Methods | Our institutional review board approved the study.Archival materials with a diagnosis of orf infection and inflamed molluscum contagiosum (I-MC) were retrieved from our dermatopathology database.A total of 5 orf and 5 comparable I-MC cases fit the inclusion criteria.As described before, 2 immunohistochemical analysis was performed on sections obtained from formalin-fixed, paraffin-embedded tissue using antibodies to BDCA-2 (mouse IgG1, clone 124B3.13,dilution 1:50; Dendritics) and myxovirus protein A (MxA) (M143, University of Freiburg, Germany; dilution 1:100). 1,2Although anti-BDCA-2 antibody is a specific PDC marker, anti-MxA antibody indirectly assesses PDC activity because MxA is an interferon (IFN)-α/β-inducible intracellular protein well established as a surrogate marker for local type I IFN production. 1,2We used a semiquantitative scoring system to assess PDC recruitment and MxA staining (Table ).Results | Demographic data and results are summarized in the Table .Although PDCs were present in all orf (Figure ) and I-MC cases, they were significantly less abundant in orf cases.Although the difference was not significant, orf cases tended to have less type I IFN production than I-MC cases.Discussion | Plasmacytoid dendritic cells exhibit plasma cell morphologic characteristics and express CD4, CD123, BDCA-2, and toll-like receptors 7 (TLR-7) and TLR-9 in endosomal compartments. 1They are capable of producing large quantities of type I IFNs against pathogenic agents. 1 They not only