Intrathecally synthesized IgG in multiple sclerosis cerebrospinal fluid recognizes identical epitopes over time

Intrathecal antibody production manifest as oligoclonal bands (OCBs) is a hallmark of multiple sclerosis (MS). Once present, OCBs can be detected in CSF throughout the lifetime of MS patients. To determine the specificity of the OCBs, we applied CSF IgG obtained from 2 consecutive lumbar punctures of 5 MS patients to screen phage-displayed random peptide libraries, and selected identical and related peptides that reacted with the paired CSF IgGs from each patient. Highly sensitive phage-mediated immuno-PCR revealed that the phage peptides bound specifically to IgG in MS CSF collected over time. IEF immunoblots also showed that these peptides were recognized by OCBs in MS CSF. We further demonstrated that the peptides represented linear epitopes, indicating that they represent natural epitopes of corresponding protein antigens. A database search combined with alanine scan mutagenesis of peptides that bound to CSF IgG from 3 MS patients revealed that they are derived from proteins including serine/threonine-protein kinase, protein ZIP2 and MHC class II. Identification of epitopes that are recognized by IgG in MS CSF over time provides a critical tool to investigate the specificity of OCBs, which may determine the cause of disease, leading to strategies for diagnostic and therapeutic intervention.