Increased Interleukin-17 in Peripheral Blood and Cerebrospinal Fluid of Neurosyphilis Patients

Background: Treponema pallidum infection evokes vigorous immune responses, resulting in tissue damage. Several studies have demonstrated that IL-17 may be involved in the pathogenesis of syphilis. However, the role of Th17 response in neurosyphilis remains unclear. Methodology/Principal Findings: In this study, Th17 in peripheral blood from 103 neurosyphilis patients, 69 syphilis patients without neurological involvement, and 70 healthy donors were analyzed by flow cytometry. The level of IL-17 in cerebrospinal fluid (CSF) was quantified by ELISA. One-year follow up for 44 neurosyphilis patients was further monitored to investigate the role of Th17/IL-17 in neurosyphilis. We found that the frequency of Th17 cells was significantly increased in peripheral blood of patients with neurosyphilis, in comparison to healthy donors. IL-17 in CSF were detected from 55.3% neurosyphilis patients (in average of 2.29 (0-59.83) pg/ml), especially in those with symptomatic neurosyphilis (61.9%). CSF IL-17 was predominantly derived from Th17 cells in neurosyphilis patients. Levels of IL-17 in CSF of neurosyphilis patients were positively associated with total CSF protein levels and CSF VDRL (Venereal Disease Research Laboratory) titers. Notably, neurosyphilis patients with undetectable CSF IL-17 were more likely to confer to CSF VDRL negative after treatment. Conclusions: These findings indicate that Th17 response may be involved in central nervous system damage and associated with clinical symptoms in neurosyphilis patients. Th17/IL-17 may be used as an alternative surrogate marker for assessing the efficacy of clinical treatment of neurosyphilis patients.