The role of SLAM receptors in antiviral immunity has been clearly documented in the X-linked lymphoproliferative syndrome, a rare immunodeficiency human disease in which impaired signalling functions of the SLAM receptors, stemming from mutations in the SAP-encoding gene, is associated with an extreme sensitivity to infection with Epstein-Barr virus [26]. The gene discussed is SH2D1A; the disease is X-linked lymphoproliferative syndrome.