Epstein-Barr virus (EBV) infection was significantly more common in SAP-deficient 10/13 (76.9%) than XIAP-deficient 2/7 (28.6%) patients, as was hypogammaglobulinemia (10/13 (76.9%) vs. 1/7 (14.3%)).
The unique bimodal intracellular SAP protein expression indicated the presence of some residual SAP-positive T cells that are able to respond to persistent Epstein-Barr virus infection and could explain the relatively mild clinical phenotype of this patient.
The signaling lymphocyte activation molecule (SLAM)-associated protein, SAP, was first identified as the protein affected in most cases of X-linked lymphoproliferative (XLP) syndrome, a rare genetic disorder characterized by abnormal responses to Epstein-Barr virus infection, lymphoproliferative syndromes, and dysgammaglobulinemia.
Although previous studies have identified defects in lymphocytes from XLP patients, the unique role of SAP in controlling EBV infection remains unresolved.
Our results with BL derived cell lines suggest that the fate of the precursor cells is decided by the expression of the proapototic SAP and EBV infection.
Thus, loss of SAP function can lead to dysregulated immune responses characterized by the uncontrolled expansion and activation of T cells independent of EBV infection.
Therefore, the down-regulation of the SAP gene by ATF5 may represent a common mechanism for the pathogenesis of HPS that is associated with either Epstein-Barr virus infection or immune disorders with dysregulated T-cell activation.
This rare disorder of immunedysregulation presents typically after Epstein-Barr virus infection and results from defects in the SAP (SLAM associated protein) gene.
Deficiency of SAP (SLAM (signaling lymphocyte activation molecule)-associated protein) protein is associated with a severe immunodeficiency, the X-linked lymphoproliferative disease (XLP) characterized by an inappropriate immune reaction against Epstein-Barr virus infection often resulting in a fatal clinical course.