Siglecs (sialic acid binding Ig-like lectins) belong to the immunoglobulin superfamily. Siglec-G is the apparent ortholog of human Siglec-10. It is expressed by mature B cells, but significant levels of transcript were also detected in DC, myeloid cells, and to a lesser extent, T cells. Mature Siglec-G consists of a 526 amino acid (aa) extracellular domain (ECD), a 21 aa transmembrane segment, and a 124 aa cytoplasmic domain. Siglec-G is a member of the CD33-related Siglec family in the mouse, and is involved in negative regulation of B-cell antigen receptor signaling and specifically acts on B1 cells to inhibit Ca2+ signaling, cellular expansion and antibody secretion.