Intracellular free Mg2+is required to maintain NKG2D expression necessary for controlling EBV infection in XMEN disease

Abstract Epstein-Barr virus (EBV) is a B cell-tropic gammaherpesvirus present in latent form in approximately 90% of people worldwide. However, a subset of immunocompromised hosts develop malignancy from uncontrolled EBV infection. While the etiology of such immunodeficiency states is sometimes apparent, as in HIV and post-transplant immunosuppression, the underlying immune deficiency is other cases remains unknown. X-linked immunodeficiency with Mg2+ defect, EBV infection, and neoplasia (XMEN) disease is a novel primary immunodeficiency characterized by deleterious mutations in magnesium transporter 1 (MAGT1), chronic EBV infection and increased susceptibility for EBV-associated lymphomas. We had previously demonstrated that MAGT1 mediates a second messenger role for Mg2+ during T cell activation. Here, we show that loss of MAGT1 also decreases the basal level of intracellular free Mg2+ and abolishes the expression of NKG2D on natural killer cells and cytotoxic T lymphocytes, leading to impaired cytotoxicity against EBV-transformed lymphoblastoid cell lines. Interestingly, both these defects can be restored in vitro and in vivo by exogenous Mg2+ supplementation, leading to decreased EBV-infected cells in vivo. This not only revealed the first specific molecular function of basal free Mg2+ in eukaryotic cells but also identified a novel Mg2+-dependent immune arm of defense against EBV lymphomagenesis that has profound diagnostic and therapeutic implications for XMEN disease.