Detection of Treponema pallidum in skin lesions of secondary syphilis and characterization of the inflammatory infiltrate

Abstract

Background: Syphilis is an ancient sexually transmitted disease. However, the pathogenesis of mucocutaneous lesions of secondary syphilis is not completely understood.

Methods: We analyzed the presence of Treponema pallidum in formalin-fixed, paraffin-embedded biopsy specimens from mucocutaneous lesions of secondary syphilis using highly sensitive nested polymerase chain reaction (PCR). The inflammatory infiltrates from the same specimens are also characterized using immunohistochemical methods.

Results and conclusions: Ten out of 24 (41.7%) specimens are T. pallidum positive using nested PCR, whereas none of them is T. pallidum positive using traditional silver staining. The presence of T. pallidum in the mucocutaneous lesions indicates that mucocutaneous lesions of secondary syphilis might be caused by direct T. pallidum invasion rather than by an allergic reaction. Furthermore, the majority of inflammatory infiltrating cells are CD45RO-positive T cells and CD68-positive macrophages, suggesting that cellular immunity plays an important role in the host reaction against T. pallidum infection in secondary syphilis.