CXCL9 and macrophage activation syndrome: Intriguingly, UDON cluster U12 showed associations of both fever (with CD16 Monocytes and pre-DCs) and CXCL9 secretion (several myeloid and lymphoid populations), comprising all patients with MAS plus one patient defined as active SJIA but noted to have subclinical MAS, further validating the clinical connection between these patients.