Page 50 - The autoimmune hypothesis of narcolepsy and its unexplored clinical features M.S. Schinkelshoek

Chapter 3
Table 3.2. Characteristics of study participants. Data indicate mean ± standard deviation. P-values result from Student’s t-tests for the continuous variables and Pearson’s chi-square tests for dichotomous variables.
N
Age (years)
Males (%)
HLA-DQ6 + Hypocretin-1 < 110pg/mL H1N1 vaccination (%)
Narcolepsy type 1
81
31.6 ± 19.2
39 (48.1%)
80/81
34/34
15/47 (32%)
Healthy controls
19
55.0 ± 8.4 9 (47.4%)
19/19
Not available Not available
p-value
<0.001 0.951
0.626
Not applicable Not applicable
48
H1N1-HA275-287, Hcrt56-68 and Hcrt87-99 presented by HLA-DQ6 show structural homology
Based on earlier described peptides of H1N1-HA and hypocretin that are able to bind HLA-DQ6 (De la Herran-Arita et al., 2013, De la Herran-Arita et al., 2014), we investigated the possibility of molecular mimicry between H1N1-HA and Hcrt peptides in the context of HLA-DQ6 presentation. We crystallized and determined the crystal structures of H1N1-HA275-287, Hcrt56-68 and Hcrt87-99 presented by HLA-DQ6 at resolutions of 1.7Å, 2.0Å and 1.95Å, respectively (Figure 3.1). Alignment of the structures revealed that the two Hcrt peptide - HLA-DQ6 complexes, HLA-DQ6-Hcrt56-68 and HLA-DQ6-Hcrt87-99, were nearly indistinguishable in terms of peptide backbone positioning (Cα rmsd <0.1Å), peptide sidechain conformations and HLA substructure surrounding the peptide. Compared to the two Hcrt complexes, the H1N1-HA275-287 peptide was bound to HLA-DQ6 in the expected homologous register and with overall similar backbone positioning (Cα rmsd <0.35Å) and sidechain conformations. Within the 9-mer core of the bound peptides, the most notable differences were observed in the exposed positions p2 and p8 of the peptides (p2-histidine and p8-threonine in the Hcrt complexes, and p2-alanine and p8-isoleucine in the H1N1-HA complex). In addition to the differences in peptide sidechains, we observed a difference in the β-chain helix, which was positioned closer to the peptide in the H1N1-HA complex when compared to the two Hcrt complexes. This homology prompted us to determine whether this could also lead to T cell cross-reactivity to the H1N1-HA and hypocretin peptides in functional experiments.