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Detection of Treponema pallidum DNA in cutaneous lesions of secondary syphilis and characterization of the inflammatory infiltrate.

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.