CD8A and Autoimmunity: As well as its role in the suppression of melatonin availability and the upregulation of the NAS/melatonin ratio, leading to the NAS activation of TrkB-T1, the AhR has several roles in the pathophysiology of ‘autoimmune’ disorders, including by increasing programmed cell death (PD)-1 expression in different cell types [144,145], including CD8+ T cells [146].