CXCL13 and neurosyphilis: Thus, the CSF/serum ratio of CXCL13 in neurosyphilis patients (median 48.35, ranged from 0.09 to 2854.3) was greatly higher than that in non-neurosyphilis patients (median 0.32, ranged from 0.02 to 13.6, p = 0.000) (Fig. 2M).