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 5

Silencing NTB-A expression reduces TCR-induced upregulation of FASL and BIM and RICD.

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Silencing NTB-A expression reduces TCR-induced upregulation of FASL and ...
(A) Activated PBLs transfected with NTB-A–specific siRNA or NS control siRNA were restimulated with increasing doses of OKT3 mAb, and apoptosis was assessed at 24 hours by PI staining. Surface expression of NTB-A was measured by flow cytometry for NS and NTB-A siRNA–transfected cells relative to cells stained with isotype control Ab. (B) PBLs transfected as described in A were restimulated with OKT3 mAb for 0 or 6 hours, then stained with Annexin V–FITC and PI. Numbers in each quadrant indicate the percentage of cells in that quadrant. (C) Real-time PCR analysis of FASLG and BIM mRNA expression in T cells transfected with NS or NTB-A–specific siRNA, following restimulation with OKT3 mAb. Results are shown as fold induction relative to untreated cells (0 hr), normalized to GAPDH expression. (D) As described in C, cells were lysed following OKT3 restimulation. Cell lysates separated by SDS-PAGE were immunoblotted with the indicated Abs. (E) ELISA detection of sFasL in supernatants collected from siRNA-transfected cells restimulated with OKT3 for 0 or 6 hours.