SH2D1A acts as an inhibitor of the signaling lymphocyte activation molecule （SLAM） self-association. The SH2D1A protein is expressed at a high level in the thymus and the lung， with a lower level of expression in the spleen and the liver. The SH2D1A protein contains an SH2 domain and a short tail. SH2D1A has a key role in the bidirectional stimulation of T and B cells. Defects in the SH2D1A gene cause the X-linked lymphoproliferative disease （XLPD）， aka Duncan disease. The XLPD is distinguished by a rare congenital immunodeficiency following an EBV infection （Epstein-Barr virus）.
