Page 74 - The autoimmune hypothesis of narcolepsy and its unexplored clinical features M.S. Schinkelshoek

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Chapter 4
patients (Hartmann et al., 2016) compared PBMCs of healthy donors and NT1 patients with other hypersomnolence disorders by mass cytometry. Of note, the panel of immune cell markers Hartmann et al. used differs from ours as they used antibodies targeting both surface antigens and cytokines, while we used only surface marker antibodies. Moreover, Hartman et al. included mostly NT1 patients several years after disease onset, so that comparisons between results of both studies should be made with caution. However, as our findings indicate, the differences in immune cell composition between NT1 patients with recent and those with later onset might well be negligible. Hartmann et al. reported multifaceted immune activation in primarily the CD4+ and CD8+ T cell compartments. This is partly reflected by our results: several populations of memory CD4+ and CD8+ T cells were found more frequently in NT1 patients compared with HLA-matched healthy controls (Supplementary table 4.2), albeit not corresponding with the population found by Hartmann et al. Since NT1 patients were included longer after disease onset in the study by Hartmann et al, they righteously mention that it remains to be established whether these changes are primarily due to an autoimmune process in NT1. A recent study that compares immune cell composition in Pandemrix®-induced NT1 patients with their healthy siblings by mass cytometry reports a lower frequency of CD8+CD27+ T cells in patients (Lind et al., 2020). Interestingly, our study shows a non-significant higher frequency of CD8+CD27+ T cells, that were mostly CD45RO- and could therefore be considered naïve CD8+ T cells (Hintzen et al., 1994). Additionally, CD8+CD27-, mostly CD45RA+, T cells were found to be increased in NT1 patients, consistent with terminally differentiated effector CD8+ T cells (TEMRA) (Hamann et al., 1999). Also the increased frequency of regulatory CD4+ T cells, consistent with earlier findings (Lecendreux et al., 2017), points to multifaceted immune activation in NT1 patients.
A limitation to our study is that we were not able to measure cerebrospinal fluid samples in addition to PBMCs. Acquiring cerebrospinal fluid samples close to disease onset is challenging, since many NT1 patients are diagnosed later after disease onset. Also, many of them already meet the criteria for NT1 without the necessity for testing hypocretin-1 in cerebrospinal fluid, which makes a lumbar puncture a redundant invasive procedure. Furthermore, the low amount of cells in cerebrospinal fluid does not allow for performing mass cytometry experiments