Expansion of CD4(dim)CD(8+) T cells characterizes macrophage activation syndrome and other secondary HLH

CD8(+) T-cell activation has been demonstrated to distinguish patients with primary and infection-associated hemophagocytic lymphohistiocytosis (HLH) from patients with early sepsis. We evaluated the activation profile of CD8(+) T cells in patients with various forms of secondary HLH (sHLH), including macrophage activation syndrome (MAS). Peripheral blood mononuclear cells from children with inactive systemic juvenile idiopathic arthritis (sJIA, n = 17), active sJIA (n = 27), MAS in sJIA (n = 14), infection-associated HLH (n = 7), and with other forms of sHLH (n = 9) were analyzed by flow cytometry. Compared with patients with active sJIA, in patients with MAS and sHLH of different origins, beside a significant increase in the frequency of CD38(high)/HLA-DR(+)CD8(+) T cells, we found a significant increase in the frequency of CD8(+) T cells expressing the CD4 antigen (CD4(dim)CD8(+) T cells). These cells expressed high levels of the activation markers CD38 and HLA-DR, suggesting they were a subset of CD38(high)/HLA-DR(+)CD8(+) T cells, as well as of the activation/exhaustion markers CD25, PD1, CD95, and interferon-g. The frequency of CD4(dim)CD8(+) T cells strongly correlated with most of the laboratory parameters of MAS severity and with circulating levels of CXCL9 and interleukin-18. These findings were confirmed in a prospective replication cohort in which no expansion of any particular T-cell receptor Vb family in CD3(+) T cells of patients with sHLH was found. Finally, frequency of CD4(dim)CD8(+), but not of CD38(high)/HLA-DR(+)CD8(+) T cells, significantly correlated with a clinical severity score, further supporting the involvement of these cells in MAS/sHLH pathogenesis.