Laboratory studies that can be used to facilitate a diagnosis of XLP. (A) Flow cytometric detection of intracellular SAP in peripheral blood CD8⁺ T cells and NK cells from a normal control, a patient with SAP deficiency, and a maternal carrier. (B) Flow cytometric detection of intracellular XIAP in peripheral blood CD8⁺ T cells and NK cells from a normal control, a patient with SAP deficiency, and a maternal carrier. (C) Flow cytometric quantification of peripheral blood NKT cells of a normal control, a patient with SAP deficiency, and a patient with XIAP deficiency (NKT cells identified as CD3⁺, TCRVα24⁺, and TCRVβ11 copositive lymphocytes). (D) Sample scatter plots measuring percentage of viable T cells after induction of RICD of activated and expanded T cells of an adult control, a patient with SAP deficiency, and a patient with XIAP deficiency using the anti-CD3 monoclonal antibody OKT3 (500 ng/mL). (E) Graphical representation of T-cell death induced by RICD. Cell death was quantified as follows: % cell loss = (1 − (% viable cells, treated/% viable cells, untreated)) × 100.