*3.1.2 SAP, XIAP, and perforin expression in Hemophagocytic lymphohistiocytosis (HLH)*

Measurement of intracellular signaling lymphocyte activation moleculeassociated protein and X-linked inhibitor of apoptosis are used as screening tools to evaluate X-linked lymphoproliferative syndrome disorder type 1 and 2, respectively. This approach has been shown to provide good sensitivity and specificity compared

with genetic mutation evaluation, and it is characterized by high negative predictive value. The lack of intracellular perforin expression in NK cells is characteristic of familial hemophagocytic lymphohistiocytosis type 2 [26, 27].

See the intracellular staining protocol in Section 3.1.
