Genomic organization and characterization of mouse SAP, the gene that is altered in X-linked lymphoproliferative disease

X-linked lymphoproliferative (XLP) disease is a fatal immunological disorde r that renders the immune system unable to respond effectively to Epstein-B arr virus (EBV) infection. The gene that encodes a protein termed SAP or SH 2D1A is either deleted or mutated in XLP patients, resulting in uncontrolle d B- and T-cell proliferation upon EBV infection. Here, we report the cloni ng and characterization of the mouse SAP gene. It is localized on the mouse X chromosome and comprises four exons spanning approximately 25 kb. Its ex pression appears to be restricted to T lymphocytes, Whereas a high level of SAP expression is observed in Th1 cells, only small amounts are detectable in Th2 cells. Moreover, SAP expression is down-regulated upon in vitro act ivation of T cells, including CD4(+), CD8(+) single-positive T cells, and T h1 and Th2 cells. This study provides valuable information for in-depth gen etic and biochemical analysis of the function of SAP in the immune system.