Antibodies in primary progressive multiple sclerosis CSF impair remyelination of lysolecithin-induced lesions

Multiple sclerosis (MS) is characterized by inflammatory demyelination, astrogliosis and axonal loss in the CNS. Most patients present with relapsing-remitting MS (RRMS) then eventually enter a phase of disease progression termed secondary progressive MS (SPMS). However, approximately 10-15% of patients diagnosed with primary progressive multiple sclerosis (PPMS) experience unremitting disease progression from disease onset. This progressive clinical course of PPMS suggests that remyelination is impaired in contrast to relapsing-remitting forms of the disease. We previously reported that intrathecal injection of cerebrospinal fluid (CSF) from PPMS patients, but not RRMS or SPMS patients, delayed spontaneous remyelination in lysolecithin-induced lesions. However, the PPMS CSF factors contributing to impaired remyelination have yet to be identified. Here, we investigated whether antibodies present in PPMS CSF are responsible for delayed remyelination of lysolecithin-induced lesions.

CSF obtained from untreated PPMS patients was passed through a tangential flow filtration system to remove components larger than 100 kDa (including antibodies). Adult C57BL/6 female mice underwent a laminectomy at cervical level 5 (C5) and 1μl of 1% lysolecithin was injected into the dorsal column. At 5 days post lysolecithin injection, mice received 3μl injections into the C5 subarachnoid space of either: 1) CSF from PPMS patients, 2) filtered PPMS CSF, or 3) PPMS or RRMS recombinant antibodies (rAbs) produced after FACS sorting B-cells in CSF then DNA sequencing IgG variable regions. Mice were perfused 12 days after lysolecithin injection. Spinal cords were post-fixed overnight in 4% paraformaldehyde, cryoprotected in 30% sucrose, then cryosectioned for histological analyses.

Luxol fast blue staining revealed significantly larger lesion volumes in PPMS CSF-injected mice compared to mice injected with filtered PPMS CSF, suggesting that the factor(s) in PPMS CSF responsible for impeding remyelination are larger than 100 kDa. Preliminary data suggest that mice injected with PPMS rAbs also have larger volumes of demyelination than mice injected with RRMS rAbs, implicating a role of antibodies in PPMS CSF in delaying remyelination. Together, these data suggest that CSF pheresis targeting antibodies may be a therapeutic option in PPMS patients.