Perforin expression in T-cell subsets from a Munc18-2–deficient patient with ongoing HLH. Freshly isolated PBMCs from healthy adult volunteers and an untreated Munc18-2–deficient patient with HLH were surface stained with fluorochrome-conjugated antibodies to CD3, CD4, CD8, CD14, CD19, CD27, CD28, CD45RA, CD45RO, CD56, and CD57, followed by fixation, permeabilization, and intracellular staining with isotype control or anti-perforin and anti-granzyme B antibodies or antibodies to perforin and granzyme B, and then analyzed by flow cytometry. (A) Plots showing CD57 versus isotype or perforin-staining on T-cell and NK cell subsets, as indicated. (B) Plots showing CD57 versus CD27 staining on T-cell subsets, as indicated. Histograms display the expression of perforin, granzyme B, CD28, CD45RA, CD45RO, and CD62L in the CD27⁺CD57⁺ and CD27⁺CD57⁻ T-cell subsets, as indicated.