Autoantibodies against distinct neuronal populations in narcoleptic patients – A possible link to vaccine induced autoimmunity?

Abstract

Introduction Narcolepsy is a neurological sleep disorder that is characterized by excessive daytime sleepiness and cataplexy. The aetiology is unknown but genetic analyses have revealed a strong link to the HLA DQB1 ∗ 06:02 and T-cell receptor alpha loci. Thus, narcolepsy is proposed to be an autoimmune disease. During 2009–2010, a link between vaccination with the adjuvanted H1N1 influenza vaccine Pandemrix and onset of narcolepsy was observed in Finland and Sweden. We hypothesized that vaccination triggered generation of autoantibodies against orexinergic neurons in the lateral hypothalamus (LH) of affected patients. We searched for autoantibodies using immunohistochemistry using a rat brain ‘neuroanatomical array’. Materials and methods Sera from 45 narcoleptic patients, 20 patients with other sleep related disorders (OSRD) and 20 healthy controls were included in the study, all of Finnish origin. All patients were HLA DQB1 ∗ 06:02 positive. Clinical information was collected. Sections of formalin- fixed rat brains were processed for immunohistochemistry using patient sera as primary antibody, followed by FITC-conjugated antibodies. Double-labelling with antisera to various relevant markers was carried out: Orexin, melanocyte-concentrating hormone (MCH), s-endorphin (marker for pro-opiomelanocortin (POMC) neurons), glutamic acid decarboxylase and more. Results Three distinct groups of immunoreactivity were recorded: group A (4/45) encompassed the MCH, but not the orexin neurons in the LH and the POMC neurons in the hypothalamic arcuate nucleus; group B (5/45) GABAergic interneurons in the cortex, many of them being calretinin or calbindin immunoreactive; and group C (4/45) neurons in the globus pallidus. In total 13/45 (29%) of narcoleptic sera stained some of the groups A, B or C. In the OSRD-group one positive serum was found (group B), whereas none of the sera in the healthy controls showed any staining. There was no clear link between the staining patterns and a previous history of Pandemrix-vaccination. Conclusion Almost one third of narcoleptic sera of Finnish patients contains autoantibodies against neuronal subpopulations, at least one of which has been associated with sleep-regulation. Acknowledgements The study was funded by the Swedish Medical Product Agency, the Swedish Research Council (VR) and Academy of Finland (26063) is a part of the NARPA- NORD consortium between Finland and Sweden.