Soluble Nogo-A in CSF is not a useful biomarker for multiple sclerosis

Objective: To determine whether the presence of Nogo-A protein in CSF is a useful biomarker for multiple sclerosis (MS). Methods: We performed Western blots on CSF from patients with MS and controls with the commercially available Nogo-A antibody and secondary antibody used in a prior report. We used densitometry to measure band density on Western blot. Controls included blots without primary antibody, samples without dithiothreitol (DTT), CSF passed through a protein G column, and Western blots with anti-Ig-light chain antibody. IgG concentration in CSF was measured by ELISA. Results: A band at about 25 kD band was detectable in almost all CSF specimens, but was darker in samples from patients with MS. The density relative to a reference sample (mean +/- SD) was 0.84 +/- 0.67 for relapsing MS (n +/- 17), 1.16 +/- 0.74 for primary progressive MS (n +/- 11), and 0.49 +/- 0.22 in controls (n +/- 12). This band was still present when the primary antibody was omitted, but was absent if the sample buffer did not include DTT or if the CSF was first adsorbed with protein G. IgG concentration was higher in MS CSF and correlated closely with the 25 kD band density (r +/- 0.78). Conclusions: A 25 kD band is detectable on Western blots stained with Nogo-A antibody in almost all CSF specimens, but is darker in MS specimens. Our results suggest this band is immunoglobulin light chains rather than Nogo-A. It is not likely to be a useful biomarker for multiple sclerosis.