Nogo-A and NfL Levels in CSF from Newly Diagnosed Multiple Sclerosis and Neuromyelitis Optica Spectrum Disorder Patients Positive for Anti-HHV6-A IgG Autoantibody

<b>Background:</b> Agents responsible for the initiation of autoimmune responses are still under investigation. The aim of this study was to determine Nogo-A and NfL levels in CSF samples from newly diagnosed multiple sclerosis (MS), neuromyelitis optica spectrum disorder (NMOSD) and pseudotumour cerebri (PTC) patients positive for HHV6-A IgG autoantibody. <b>Methods:</b> Initial CSF samples from 42 patients were analysed by ELISA. Independent samples t tests, Mann-Whitney U tests, crosstabulation with Fisher's exact tests and Pearson/Spearman correlation analyses were used for group comparisons. <b>Results:</b> Anti-HHV6A IgG positivity was highest in MS, followed by NMOSD and then PTC (6.7%), but no significant difference in positivity was found among the groups (<i>p</i> = 0.367). No significant difference was found among the groups for NfL or Nogo-A levels (<i>p</i> = 0.373, <i>p</i> = 0.975, respectively). Anti-HHV6A negative MS cases had lower Nogo-A levels than positive cases (<i>p</i> = 0.046). In addition, anti-HHV6A negative PTC cases had lower Nogo-A levels than positive cases (<i>p</i> = 0.015). Anti-HHV6A positive MS patients had lower Nogo-A levels than the PTC positive group and this difference was very close to significant (<i>p</i> = 0.063). <b>Conclusions:</b> Anti-HHV6A positivity was found mainly in the MS group. Anti-HHV6A was found to be associated with Nogo-A levels, especially in the MS and PTC groups. Anti-HHV6A autoantibodies might play a role in the pathophysiology of MS.