IMMUNODEFICIENCIES CHARACTERIZED BY INCREASED SUSCEPTIBILITY TO EBV INFECTIONS
XLP is a rare inherited immunodeficiency characterized by life-threatening pathological process triggered by EBV infections. The manifestations of this conditions include fulminant infectious mononucleosis, virally induced HLH, hypogammaglobulinemia, and the propensity to develop malignant lymphomas. Mutation in the gene SH2D1A encoding the signaling lymphocyte activation molecule (SLAM) associated protein (SAP) are responsible for more than 60% of cases XLP. SH2D1A-/- mice lack NK T cells and this defect could be corrected by reconstitution of SH2D1A expression within bone marrow cells derived from SH2D1A-/- mice. Patients with XLP also lack NK T cells. Therefore, it is possible that NK T-cell function is essential for controlling EBV infection as well as homeostasis of T-cell responses to this virus. Further support for this theory comes from the recent observation that XLP can also be caused by a mutation in the gene (BIRC4) that encodes for the protein X-linked inhibitor of apoptosis (XIAP). XIAP-/- patients also have reduced numbers of NK T cells.