Autoimmunity to hypocretin and molecular mimicry to flu antigens in Type 1 narcolepsy

Abstract

Abstract Type 1 narcolepsy (T1N) is caused by hypocretin (HCRT) neuronal loss. Association with the Human Leukocyte Antigen (HLA)-DQB1*06:02/DQA1*01:02 (98% vs 25%) heterodimer (DQ0602), T cell receptor (TCR) and other immune loci suggest autoimmunity but autoantigen(s) are unknown. Onset is seasonal and associated with influenza A, notably pandemic 2009 H1N1 (pH1N1). An extensive unbiased DQ0602 binding peptide screen was performed encompassing peptides derived from Pandemrix ® X-179-A pH1N1 influenza-A vaccine, a known T1N trigger, other H1N1 strains, and potential human autoantigens HCRT and RFX4, identifying 109 binders. The presence of cognate tetramer-peptide specific CD4 + T cells was studied in 35 narcolepsy cases and 22 DQ0602 controls after expansion of antigen-specific cells in Peripheral Blood Monocytes Cell (PBMC) cultures. Higher reactivity to influenza epitopes pHA 273-287 (pH1N1 specific) and PR8 (H1N1 pre 2009)-specific NP 17-31 were observed in T1N. Extensive reactivity to C-amidated but not native version of HCRT 54-66 and HCRT 86-97 , which are two highly homologous peptides (HCRT NH2 ) was observed with higher frequencies of specific T cells in T1N. TCRα/β CDR3 sequences found in pHA 273-287, NP 17-31 and HCRT NH2 tetramer positive CD4 + cells were also retrieved in single INFγ-secreting CD4 + sorted cells stimulated with Pandemrix ® , confirming immunodominance and functional significance in DQ0602-mediated responses and molecular mimicry. TCRα/β CDR3 motifs of HCRT 54-66 and HCRT 86-97 tetramers were extensively shared. Particularly notable was sharing across subjects of an CDR3α, CAVETDSWGKLQF (in association with various CDR3β that used TRAJ24, a chain modulated by Single Nucleotide Polymorphism (SNPs) rs1154155 and rs1483979 associated with T1N. Sharing of CDR3β CASSQETQGRNYGYTF (in association with various CDR3α was also observed with HCRT NH2 and pHA 273-287 -tetramers across subjects. This segment uses TRBV4-2, a segment modulated by narcolepsy-associated SNP rs1008599. Higher HCRT NH2 positive CD4 + T cell numbers in T1N together with sharing of J24 CAVETDSWGKLQF in HCRT NH2 autoimmune responses, indicates causal DQ0602-mediated CD4 + autoreactivity to HCRT in T1N. Our results provide evidence for autoimmunity and molecular mimicry with flu antigens modulated by genetic components in the pathophysiology of T1N.