Increased numbers of CD4+ T-cells in hypocretin/orexin region of Narcolepsy Type 1

Narcolepsy type 1 (NT1) is proposed to be an autoimmune disorder targeting hypothalamic hypocretin (orexin, Hcrt) neurons. Hcrt reactive T-cells have been identified in blood and cerebrospinal fluid (CSF) of NT1 patients. However, it remains unknown whether T-cells infiltrate the brain. Since T-cells can be retained for a lifetime in tissues as tissue resident memory T-cells after primary antigen exposure, we now systematically assess the presence of CD4+ and CD8+ T-cells in NT1 brains to determine their regional distribution and potential autoimmune involvement in NT1 neuropathology. We immunohistochemically stained and quantified CD4+ and CD8+ T-cells in post-mortem brain tissue of NT1 patients (n=5) and matched controls (n=5) in the Hcrt region, paraventricular nucleus (PVN) and median eminence (ME) as well as in the substantia nigra (SN) and locus coeruleus (LC). To phenotypically characterize CD4+ T-cells, we performed double staining with CD49a or C-X-C chemokine receptor type 6 (CXCR6). Furthermore, we stained for fibrinogen to estimate blood-brain barrier integrity, as well as microglia markers and an astrocyte marker to evaluate acute immune reactivity in the Hcrt region of NT1 brains. In NT1 there was an 11-fold increase in total number of CD4+ T-cells in the Hcrt region, but not in the PVN, ME, nor SN or LC. These CD4+ T-cells exhibited tissue residential memory features with double staining with CD49a or CXCR6. There were no changes in blood-brain barrier integrity, microglia and astrocyte staining intensities between NT1 and controls. In addition, the total number of CD4+ T-cells in the Hcrt region showed significant negative correlations with mean sleep latency in NT1 cases. Our findings suggest an enrichment of CD4+ T-cells specifically in the Hcrt region of NT1 indicating prior local antigen engagement. Moreover, greater CD4+ T-cell presence in the Hcrt region of NT1 was associated with increased symptom severity, as reflected by shorter sleep latency. These data support the hypothesis that CD4+ T-cells infiltrate the Hcrt region, where they may contribute to the autoimmune process that initiates NT1.