Page 117 - The autoimmune hypothesis of narcolepsy and its unexplored clinical features M.S. Schinkelshoek

Chapter 3 describes our study on CD4+ T cells that cross-react with H1N1 influenza and hypocretin peptides. In this study we show that HLA- DQB1*06:02-restricted CD4+ T cell responses against H1N1 influenza peptides are more frequent in NT1 patients than in controls. However, we did not identify any hypocretin peptide-specific CD4+ T cell responses and, thus, no cross-reactivity between H1N1 and hypocretin. This argues against a causal role for these H1N1 peptides in the autoimmune pathogenesis of NT1.
In contrast to our findings, several studies do report the presence of CD4+ and CD8+ T cells that recognize hypocretin (Cogswell et al., 2019, Latorre et al., 2018, Pedersen et al., 2019, Jiang et al., 2019) or show cross-reactivity to hypocretin and H1N1 influenza peptides (Luo et al., 2018). One of the reasons for this discrepancy may be the different techniques that were used. In Chapter 3, we focus specifically on reactivity to H1N1 influenza and hypocretin peptide fragments that were chosen based on their structural resemblance as assessed by crystallography. All other studies used broad peptide pools or peptide libraries, thereby decreasing specificity, but largely increasing the possibility of finding a response.
Moreover, we validated the supposed specificity of expanded cells in T cell cultures with the H1N1 influenza and hypocretin peptides. We assessed proliferation of T cell clones generated from these T cell cultures, upon a challenge with a hypocretin or H1N1 influenza peptide fragment. This essential step was not performed in two of the aforementioned studies (Luo et al., 2018, Cogswell et al., 2019), thereby rendering conclusions about the specificity of T cell cultures in those latter studies uncertain.
The authors of the first study (Luo et al., 2018) responded to our study in the Journal of Neuroimmunology (Mignot et al., 2019). Firstly, they stress the importance of performing experiments with C-amidated peptides, since they only demonstrated cross-reactivity between hypocretin and H1N1- haemagglutinin peptides when hypocretin peptides were C-amidated. We have unfortunately not been able to repeat our experiments with these peptides to ascertain whether this difference indeed explains the differences between the outcomes of both studies. Secondly, Mignot et al. state that the conclusion that we could not find evidence for molecular mimicry with the peptides tested, was premature, because our sample size would not allow for detecting cross- reactivity to begin with, as we only measured 33 T cell clones. We do not agree with this comment. In our publication, we tested peripheral blood of 81 NT1
Summary, discussion and future perspectives
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