Objective: To investigate the possible mechanism of the cutaneous lesion formation in secondary syphilis and role of cellular immunity in the pathogenesis of syphilis.
Methods: Treponema pallidum DNA was detected in 24 formalin-fixed, paraffin-embedded skin specimens from lesions of secondary syphilis by nested PCR. The inflammatory infiltrate in the cutaneous lesions of secondary syphilis was investigated using immunohistochemical technique.
Results: The TP-specific DNA was found in 10 of 24 (45.8%) lesions of secondary syphilis. However, no Treponema pallidum were found in all 24 tissue section samples when silver staining was performed. CD45RO (+) Tcells were found in all syphilis lesions with strong staining. CD68 (+) cells were found in 68.2% of the skin specimens. Meanwhile, a few CD20 (+) cells and CD57 (+) cells were seen in the infiltrates.
Conclusion: The cutaneous lesions might be formed by invasion of TP to skin rather than an allergic reaction. The predominant T cells and macrophages infiltrating in secondary syphilitic lesions indicate that cellular immunity might play a critical role in host reaction against TP infection.