Autoimmunity to hypocretin and molecular mimicry to flu in type 1 narcolepsy

Type 1 narcolepsy (T1N) is caused by hypocretin/orexin (HCRT) neuronal loss. Association with the HLA DQB1*06:02/DQA1*01:02 (98% vs. 25%) heterodimer (DQ0602), T cell receptors (TCR) and other immune loci suggest autoimmunity but autoantigens are unknown. Onset is seasonal and associated with influenza A, notably pandemic 2009 H1N1 (pH1N1) infection and vaccination (Pandemrix). Peptides derived from HCRT and influenza A, including pH1N1, were screened for DQ0602 binding and presence of cognate DQ0602 tetramer-peptide-specific CD4(+) T cells tested in 35 T1N cases and 22 DQ0602 controls. Higher reactivity to influenza pHA(273-287) (pH1N1 specific), PR8 (H1N1 pre-2009 and H2N2)-specific NP17-31 and C-amidated but not native version of HCRT54-66 and HCRT86-97 (HCRTNH2) were observed in T1N. Single-cell TCR sequencing revealed sharing of CDR3 beta TRBV4-2-CASSQETQGRNYGYTF in HCRTNH2 and pHA(273-287)-tetramers, suggesting molecular mimicry. This public CDR3 beta uses TRBV4-2, a segment modulated by T1N-associated SNP rs1008599, suggesting causality. TCR-alpha/beta CDR3 motifs of HCRT54-66-NH2 and HCRT86-97-NH2 tetramers were extensively shared: notably public CDR3 alpha, TRAV2-CAVETDSWGKLQF-TRAJ24, that uses TRAJ24, a chain modulated by T1N-associated SNPs rs1154155 and rs1483979. TCR-alpha/beta CDR3 sequences found in pHA(273-287), NP17-31, and HCRTNH2 tetramer-positive CD4(+) cells were also retrieved in single INF-gamma-secreting CD4(+) sorted cells stimulated with Pandemrix, independently confirming these results. Our results provide evidence for autoimmunity and molecular mimicry with flu antigens modulated by genetic components in the pathophysiology of T1N.