CXCL13 and neurosyphilis: Thus, we assessed the efficacy of combined CSF CXCL13, CXCL10 and CXCL8 (Model 1) and combined the ratio of CSF/serum CXCL13, CXCL10 and CXCL8 (Model 2) as biomarkers for diagnosis of neurosyphilis.