Data collection

Intrathecal Immunoglobulin Synthesis was defined as either elevated IgG index or positive OCBs. The IgG index was calculated from the ratio of IgG CSF/serum quotient and albumin CSF/serum quotient and was defined as elevated with a ratio higher than 0.7. The amount of IgG and albumin in CSF and serum samples was measured by nephelometry (analyzer used: BN ProSpec System from Siemens Healthineers). CSF specific OCBs were mostly (n = 99) determined by isoelectric focusing followed by silver staining, only in a few samples (n = 37) that were measured later an immunoblot was carried out (gel used for both methods: polyacrylamidgel, exactly IEFGel 6–11 24S from edc Tübingen). Conventionally, OCB type 2 (OCBs in CSF only) and 3 (OCBs in CSF and serum, with additional OCBs in CSF) were defined positive [16]. Blood-CSF barrier (BCB) dysfunction was estimated by albumin CSF/serum quotient. CXCL13 concentrations were measured by ELISA test (R&D, DY801, DuoSet ELISA) according to the manufacturer instructions. We could measure CXCL13 levels in 83 of our AIS samples and values above the cut-off level of 8,6 pg/ml were defined as elevated. The measurements also included positive samples (N = 5) and negative controls (n = 5), previously measured during the routine diagnostic work up of patients. All measurements were within the expected concentration range, longitudinal measurements of the same samples did not differ more than 10%. In general, the CSF was usually freshly analyzed, cryopreserved material was only used for the re-determined samples.

Stroke localization (cortical, subcortical, infratentorial), side (right, left, both) and vascular territory (anterior and/or posterior circulation) were determined mainly on basis of cerebral imaging using either cerebral CT or if available MRI. Infarct volume was calculated with ABC/2 and summed up in case of multiple lesions, on the basis of cerebral CT or if available MRI using the diffusion weighted or T2 FLAIR sequences.

Infarct etiology was assessed by cardiovascular evaluation classified according to TOAST criteria [17].