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 6

NTB-A influences TCR-induced apoptosis signals through competitive association with SAP and SHP-1.

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NTB-A influences TCR-induced apoptosis signals through competitive assoc...
(A) NTB-A was immunoprecipitated from PBL lysates after a short time course of OKT3 restimulation. Immunoprecipitates were separated by SDS-PAGE and immunoblotted for the presence of SAP and NTB-A. SAP expression in input lysates is shown at bottom for comparison. (B) SAP was immunoprecipitated from PBL lysates and immunoblotted as described in A. (C) Cells were stained with mAbs detecting CD3 (OKT3, green) and NTB-A (red) and left on ice (4°C) or warmed to 37°C for 30 minutes. Left: Cells were imaged by confocal microscopy, with nuclei counterstained in blue. Right: Quantitative analysis based on counting more than 200 cells from multiple fields. (D) NTB-A was immunoprecipitated from lysates prepared from normal donor or XLP Pt4 PBLs following OKT3 stimulation. Immunoprecipitates were separated by SDS-PAGE and immunoblotted for the presence of SHP-1 and NTB-A. (E) Normal donor or XLP Pt4 PBLs were transfected with NS, SHP-1–specific, or SHP-2–specific siRNA and restimulated with increasing doses of OKT3 mAb. Apoptosis was measured by PI staining. Knockdown efficiency was assessed by immunoblotting. (F and G) Normal donor or XLP PBLs were transfected with NS or NTB-A siRNA and restimulated with 100 ng/ml OKT3 mAb. Apoptosis was measured by Annexin V (F) or PI staining (G). *P < 0.04.