SH2 domain-containing protein 1A (SH2D1A / SAP) is a 128 amino acid protein, containing a single Src homology 2 (SH2) domain, flanked by 5 amino acids at the N-terminus and 25 amino acids at the C-terminus. The absence of a catalytic domain and the presence of an SH2 domain suggest that SH2D1A regulates one or more signal transduction pathways. SH2D1A interacts with signaling lymphocytic activation molecule (SLAM), which is a transmembrane protein expressed on the surface of activated T and B cells. SH2D1A (SAP) interacts via its SH2 domain with a motif (TIYXXV) present in the cytoplasmic tail of the cell-surface receptors, including CD15 / SLAM, CD84, CD229 / Ly-9, and CD244 / 2B4. SH2D1A was expressed in EBV-carrying, tumor phenotype representative (type I), but not in EBV-carrying lymphoblastoid cell line (LCL)-like (type III) or EBV-negative Burkitt lymphoma (BL) lines. It has been supposed to be related to the X-linked lymphoproliferative disease which is also known as Duncan's disease or Purtilo syndrome.