Although NK cell and CD8+ T cell numbers are normal in XMEN patients, reduced intracellular Mg++ abrogates NKG2D receptor expression on activated NK cells and CD8+ T cells, which compromises cytolytic responses against EBV+ B cells (51, 66–68). Here, CD8A is linked to X-linked immunodeficiency with magnesium defect, Epstein-Barr virus infection and neoplasia.