Clonally expanded populations of peripheral CNS-reactive T cells, characterised by increased proliferation and pro-inflammatory cytokine release (IFNγ, IL-17, GM-CSF) in response to CNS antigens relative to healthy controls, have been observed in patients with MS, NMOSD and neuropsychiatric systemic lupus erythematosus (SLE) [44, 142, 166]. Here, IL17A is linked to myeloid sarcoma.