NEFL and primary progressive multiple sclerosis: Therefore, this exploratory study was conducted to investigate whether and how PPMS patients, depending on their MRZR status (positive MRZR result (MRZR+) versus negative MRZR result (MRZR-)), differ regarding clinical disease severity and CSF biomarkers of B cell activity, neuroaxonal damage (neurofilament light chain (NfL)) and glial activity (chitinase-3-like protein 1 (CHI3L1) and glial fibrillary acidic protein (GFAP)).