CD48 is a GPI-linked protein in the CD2 family of immunoglobulin superfamily proteins. CD48 is expressed on most lineage-committed hematopoietic cells but not on hematopoietic stem cells or multipotent hematopoietic progenitors. Among dendritic cells (DC), CD48 is selectively expressed on circulating myeloid DC and resident bone marrow and thymus DC. CD2, 2B4, and heparan sulfate function as CD48 ligands. CD48 is competent to transduce signals and can also trigger signaling through CD2 or 2B4. CD48 expressed on NK cells is coactivating, whereas CD48 expressed on other cell types inhibits NK cell activation.