Expression of SIRPβ2 in peripheral blood and activated NK cells. SIRPβ2 is expressed on CD4⁺ T cells, CD8⁺ T cells, and a few CD20⁺ B cells. Notably, SIRPβ2 is expressed on a subset of CD56^dim cells, which express CD3 and correspond to NKT cells (data not shown), but not on CD56^dim resting NK cells. SIRPβ2 is also expressed on CD56^bright cells, which do not express CD3 and correspond to an NK cell subset. PBMCs and activated NK cells were stained with antibodies against CD2, CD3, CD8, CD4, CD20, CD56 (all mouse IgG2a or IgG2b), and SIRPβ2 (mouse IgG1) followed by PE- and biotin-labeled goat antimouse IgG2a/b and IgG1 antibodies, respectively, and streptavidin-allophycocyanin. NK cells were activated in vitro with IL-2, PHA, and feeder cells and stained with anti-SIRPβ2 mAb.