Analysis of female XLP carriers with heterozygous expression of SAP revealed that while memory CD8 T cells specific for cytomegalovirus or influenza can be SAP-expressing or SAP-deficient, EBV-specific T cells are exclusively SAP+ due to NTB-A- and 2B4-mediated inhibitory signaling in the absence of SAP when ligands of these SLAM receptors are engaged on antigen-bearing B cells (Palendira et al., 2011). The gene discussed is SH2D1A; the disease is influenza.