NK-cell degranulation assays are normal in most patients with FHL2, XLP, and secondary HLH. Results of CD107a degranulation assays using resting NK cells (A-C) and IL-2–activated NK cells (D-F) from patients with FHL2 (A,D), XLP1 and XLP2 (B,E), or secondary HLH (2° HLH; C,F). In panels A and C, closed symbols represent patients manifesting with HLH before age 2 and open symbols indicate manifestation of HLH after age 2. In panels B and E, triangles represent patients with XLP1 and circles represent patients with XLP2. For additional explanations, see legend to Figure 2.