The perforin-staining pattern in a healthy control and in patients with HLH.

(A) Flow cytometric analysis of perforin expression in blood cytotoxic cells from a healthy adult. A normal percentage of perforin expression in NK cells in adults was 92% ± 6%. In CD8⁺ T cells, it was 8% to 28% in adults. In CD56⁺ T cells, it was 30% to 77% in adults. (B) The most complete perforin deficiency was seen in patient P1 with primary HLH. The perforin-staining pattern showed no difference from the isotype control in all cell types. (C) The partial perforin deficiency was seen in patient P10 with primary HLH. The perforin positivity in NK cells was moderately decreased and the perforin positivity in CD8⁺ and CD56⁺ T cells was extremely decreased. (D) The percentage of NK cells in P3, a patient with EBV-associated HLH, was 3%, and NK function was extremely decreased. The perforin positivity was markedly increased in CD8⁺ and CD56⁺ T cells.