CD244 and X-linked lymphoproliferative syndrome: A role for 2B4 was actually revealed by the severe consequences of primary EBV infection in individuals suffering from X-linked lymphoproliferative disease (XLP-1), a congenital immunodeficiency in which SAP is absent or defective (Sayos et al., 1998), resulting in inhibitory signals from 2B4 impairing NK-mediated B-EBV elimination (Parolini et al., 2000).