With this study, we provide evidence that CXCL13 does not enter CSF from blood, a finding of high relevance regarding the potential of CSF CXCL13 as diagnostic, prognostic, severity, and treatment response marker for neuroinflammatory conditions such as LNB, CNS lymphoma, demyelinating CNS diseases, and neuroinfections, and regarding a potential caveat when calculating CSF/serum CXCL13 quotients [8, 18–20, 29]. Here, CXCL13 is linked to primary central nervous system lymphoma.