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 4

Loss of SAP expression impairs TCR-induced upregulation of FASL and BIM.

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Loss of SAP expression impairs TCR-induced upregulation of FASL and BIM....
(A) Microarray analysis of gene expression differentially affected by 6-hour TCR restimulation with or without silencing of SAP expression. Genes with an average of 2-fold higher (357 genes) or 50% lower (90 genes) expression in NS siRNA-transfected cells relative to SAP siRNA-transfected cells are displayed in the heat map dendrogram, with select genes highlighted. (B) Real-time PCR analysis of FASLG and BIM mRNA expression in T cells transfected with NS (black) or SAP-specific (gray) siRNA, following restimulation with OKT3 mAb. Results are shown as fold induction relative to untreated cells (0 hr), normalized to GAPDH expression at each time point. Data represent the mean ± SD for triplicate wells. (C) As described in B, cells were lysed following OKT3 restimulation. Cell lysates separated by SDS-PAGE were immunoblotted with the indicated Abs. BIM Ab detected all 3 protein isoforms (extra-long [EL], long [L], and short [S]); FasL Ab detected FL and a cytosolic N-terminal fragment (NTF). (D) Real-time PCR analysis of FASLG and BIM mRNA expression in activated T cells from a normal donor (black) and XLP Pt4 (gray) following restimulation as described in B. (E) As described in D, cells were lysed following OKT3 restimulation. Cell lysates separated by SDS-PAGE were immunoblotted with the indicated Abs. (F) ELISA detection of soluble FasL (sFasL) in supernatants collected from cells restimulated as described above for 0 or 8 hours.