Percentage of CD4^dimCD8⁺ T cells is significantly increased in patients with all forms of secondary HLH and reliably distinguishes patients with MAS from those with active sJIA. (A) Representative FACS profile showing the percentage of CD4^dimCD8⁺ T cells, gated on CD3⁺ cells, in each group of patients. Results obtained in mononuclear cells isolated from bone marrow of 3 patients with primary HLH (BM pHLH) are also reported. (B) Percentage of CD4^dimCD8⁺ T cells, gated on CD3⁺ cells, in the different patient groups. Patients who were receiving glucocorticoids longer than 2 weeks are reported as filled squares. ***P ≤ .001. (C) ROC curve analysis of CD4^dimCD8⁺ T cells was performed comparing patients with MAS/sHLH (n = 30) and patients with active sJIA (n = 27).