The FCGR2B gene spans a 15kb genomic region; Gene orientation : centromere - 3 FCGR2B 5 - telomere; 8 exons (denoted S1, S2, EC1, EC2, TM, IC1, IC2, IC3). S1 and S2 encode the signal peptide domain, EC1 and EC2 encode the extracellular domain, TM encodes the transmembrane domain and IC1, IC2, IC3 encode the intracytoplasmic region.

1.7kb mRNA. Two alternately spliced mRNA exist in humans; FcgRIIb1 and FcgRIIb2 (a 19 aa insertion encoded by IC1 is present in b1 but not in b2).

called Fc gamma RIIB

40kD transmembrane glycoprotein that possesses an intracytoplasmic Immunoreceptor Tyrosine-based Inhibition Motif (ITIM) (encoded by IC3).

B, myeloid and mast cells.

Transmembrane.

Low affinity IgG Fc receptor. Founding member ITIM family of immune inhibitory receptors. Fc gamma RIIB functions to down-regulate activatory responses mediated by Immunoreceptor Tyrosine-based Inhibition Motif (ITAM) bearing receptors such as the B-cell receptor on B cells. For example, on B-cells, negative regulation of B-cell receptor activatory signalling is initiated through co-recruitment of BCR and Fc gamma RIIB to IgG/ immune complexes. This leads to tyrosyl phosphorylation of the Fc gamma RIIB ITIM motif / recruitment of the inositol phosphatase SHIP and activation of the adaptor protein Dok - these events ultimately lead to the inhibition of ITAM-dependant Ca++ mobilisation and cellular proliferation (reduced MAPK signalling), respectively.
A proapoptotic signal through the Fc gamma RIIB transmembrane sequence has been described in conditions of homo-aggregation of Fc gamma RII on murine B cells.

Contains two immunoglobulin-like C2 domains.