Absence of autoreactive CD4+ T-cells targeting HLA-DQA1*01:02/DQB1*06:02 restricted hypocretin/orexin epitopes in narcolepsy type 1 when detected by EliSpot

- Narcolepsy type 1 is a suspected autoimmune sleep disorder associated with HLA-DQB1*06:02
- The hypocretin/orexin producing neurons are selectively destroyed.
- Genetic association points the involvement of CD4+ T-cells.
- Five epitopes from the hypocretin precursor are predicted to bind MHC DQA1*01:02/DQB1*06:02.
- CD4+ T-cells from narcolepsy type 1 patients targeting these epitopes are not detected by EliSpot.

Narcolepsy type 1, a neurological sleep disorder strongly associated with Human Leukocyte Antigen (HLA-)DQB1*06:02, is caused by the loss of hypothalamic neurons producing the wake-promoting neuropeptide hypocretin (hcrt, also known as orexin). This loss is believed to be caused by an autoimmune reaction. To test whether hcrt itself could be a possible target in the autoimmune attack, CD4+ T-cell reactivity towards six different 15-mer peptides from prepro-hypocretin with high predicted affinity to the DQA1*01:02/DQB1*06:02 MHC class II dimer was tested using EliSpot in a cohort of 22 narcolepsy patients with low CSF hcrt levels, and 23 DQB1*06:02 positive healthy controls. Our ELISpot assay had a detection limit of 1:10,000 cells.We present data showing that autoreactive CD4+ T-cells targeting epitopes from the hcrt precursor in the context of MHC-DQA1*01:02/DQB1*06:02 are either not present or present in a frequency is < 1:10,000 among peripheral CD4+ T-cells from narcolepsy type 1 patients.

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