Patient NK cells as well as CD8+CD57+ T cells displayed reduced exocytosis (Fig. 1F; normal range (mean ± 2SD) for induction of CD107a on NK cells was for K562 cell or anti-CD16 stimulation 9–41% and 30–66%, respectively, and for that on CD8+CD57+ T cells 28–76%, in healthy adults), but not abolished as frequently observed in FHL [3, 7]. Here, CD8A is linked to hemophagocytic syndrome.