there are two major forms of fcgr2b existing (fcgr2b1 and fcgr2b2) and they are created by mrna splicing mechanism, which results in the inclusion (fcgr2b1) or exclusion (fcgr2b2) of the c1 exon sequence. the presence of the c1 exon sequence (in fcgr2b1) results in tethering to the membrane of b cells, whereas its absence (in fcgr2b2) allows fast internalization of the receptor in myeloid cells. both forms contain the immunoreceptor tyrosine-based inhibitory motif (itim) in their cytoplasmic regions. the extracellular domains are 95% identical to the domains of fcgr2a and almost completely identical to the fcgr2c (the other members of cd32 family).