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Proc Natl Acad Sci U S A. 2003 Sep 2;100(18):10388-92. Epub 2003 Aug 14.

B7x: a widely expressed B7 family member that inhibits T cell activation.

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  • 1Howard Hughes Medical Institute, Department of Molecular and Cell Biology, Cancer Research Laboratory, University of California, Berkeley, CA 94720, USA.


B7 family proteins provide costimulatory signals that regulate T cell responses. Here we report the third set of B7 family-related T cell inhibitory molecules with the identification of a homolog of the B7 family, B7x. It is expressed in immune cells, nonlymphoid tissues, and some tumor cell lines. B7x inhibits cell-cycle progression, proliferation, and cytokine production of both CD4+ and CD8+ T cells. B7x binds a receptor that is expressed on activated, but not resting T cells that is distinct from known CD28 family members. Its receptor may be a recently identified inhibitory molecule, B and T lymphocyte attenuator. These studies identify a costimulatory pathway that may have a unique function in downregulation of tissue-specific autoimmunity and antitumor responses.

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