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 2

Silencing SAP expression in normal T cells results in defective RICD.

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Silencing SAP expression in normal T cells results in defective RICD. (A...
(A) Left: Activated PBLs were transfected with SAP-specific siRNA or NS control siRNA and cultured in IL-2 for an additional 4 days, then restimulated with increasing doses of OKT3 mAb. Alternatively, CD4+ or CD8+ T cells were purified from PBLs prior to siRNA transfection. Cell death at 24 hours was assessed by PI staining and measured by flow cytometry. Right: Lysates prepared from siRNA-transfected cells were separated by SDS-PAGE and immunoblotted with SAP Ab to assess knockdown of SAP expression. β-Actin served as a loading control. (B) Activated PBLs were transfected with siRNA and cultured as described above. Cells were then 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. (C) siRNA-transfected PBLs were restimulated as described above for 24 hours or left untreated, then stained with DiOC6 or anti–caspase-3 Ab. Numbers indicate the percentage of cells with permeabilized mitochondria (DiOC6lo) or active caspase-3 after restimulation.