Adhesion of human T cells to antigen-presenting cells through SIRP 2-CD47 interaction costimulates T-cell proliferation

Signal-regulatory proteins (SIRPs) are transmembrane glycoproteins belonging to the immunoglobulin (Ig) superfamily that are expressed in the immune and central nervous systems. SIRP binds CD47 and inhibits the function of macrophages, dendritic cells, and granulocytes, whereas SIRP 1 is an orphan receptor that activates the same cell types. A recently identified third member of the SIRP family, SIRP 2, is as yet uncharacterized in terms of expression, specificity, and function. Here, we show that SIRP 2 is expressed on T cells and activated natural killer (NK) cells and, like SIRP , binds CD47, mediating cell-cell adhesion. Consequently, engagement of SIRP 2 on T cells by CD47 on antigen-presenting cells results in enhanced antigen-specific T-cell proliferation. (Blood. 2005;105: 2421-2427)