Restimulation-induced apoptosis of T cells is impaired in patients with X-linked lymphoproliferative disease caused by SAP deficiency
Andrew L. Snow, … , Jack J. Bleesing, Michael J. Lenardo
Andrew L. Snow, … , Jack J. Bleesing, Michael J. Lenardo
Published September 14, 2009
Citation Information: J Clin Invest. 2009;119(10):2976-2989. https://doi.org/10.1172/JCI39518.
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Research Article Immunology

Restimulation-induced apoptosis of T cells is impaired in patients with X-linked lymphoproliferative disease caused by SAP deficiency

Abstract

X-linked lymphoproliferative disease (XLP) is a rare congenital immunodeficiency that leads to an extreme, usually fatal increase in the number of lymphocytes upon infection with EBV. It is most commonly defined molecularly by loss of expression of SLAM-associated protein (SAP). Despite this, there is little understanding of how SAP deficiency causes lymphocytosis following EBV infection. Here we show that T cells from individuals with XLP are specifically resistant to apoptosis mediated by TCR restimulation, a process that normally constrains T cell expansion during immune responses. Expression of SAP and the SLAM family receptor NK, T, and B cell antigen (NTB-A) were required for TCR-induced upregulation of key pro-apoptotic molecules and subsequent apoptosis. Further, SAP/NTB-A signaling augmented the strength of the proximal TCR signal to achieve the threshold required for restimulation-induced cell death (RICD). Strikingly, TCR ligation in activated T cells triggered increased recruitment of SAP to NTB-A, dissociation of the phosphatase SHP-1, and colocalization of NTB-A with CD3 aggregates. In contrast, NTB-A and SHP-1 contributed to RICD resistance in XLP T cells. Our results reveal what we believe to be novel roles for NTB-A and SAP in regulating T cell homeostasis through apoptosis and provide mechanistic insight into the pathogenesis of lymphoproliferative disease in XLP.

Authors

Andrew L. Snow, Rebecca A. Marsh, Scott M. Krummey, Philip Roehrs, Lisa R. Young, Kejian Zhang, Jack van Hoff, Deepali Dhar, Kim E. Nichols, Alexandra H. Filipovich, Helen C. Su, Jack J. Bleesing, Michael J. Lenardo

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Figure 1

XLP patient T cells deficient for SAP expression are resistant to RICD.

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XLP patient T cells deficient for SAP expression are resistant to RICD. ...
(A) Lysates prepared from activated PBLs were separated by SDS-PAGE and immunoblotted with SAP Ab. β-Actin served as a loading control. (B) Activated T cells were tested for sensitivity to apoptotic stimuli, including TCR restimulation using anti-CD3 (OKT3) mAb, agonistic anti-Fas APO1.3 mAb, and staurosporine (STS) and UV irradiation, or IL-2 withdrawal. Patient cells (gray) were studied in parallel with normal controls (black; C1–C3) isolated and activated on the same day. Cell loss was measured 24 hours after treatment with propidium iodide (PI) staining and flow cytometry. (C) Activated T cells cultured as described in B were restimulated with 200 ng/ml OKT3 mAb for 8 and 24 hours or left untreated (0 hr), then stained with Annexin V–FITC and PI. The numbers in each quadrant indicate the percentage of cells in that quadrant. NC, normal control. (D) Activated T cells were restimulated as above for 24 hours or left untreated, then stained with DiOC6 to measure mitochondrial membrane potential (top) or with an Ab for detection of intracellular activated caspase-3 (bottom). The numbers indicate the percentage of cells with permeabilized mitochondria (DiOC6lo) or active caspase-3 after restimulation. (E) CD4+ and CD8+ T cells were purified from activated PBLs (left) or naive PBMCs (right) and then activated. RICD sensitivity was assessed as described in B.