cγRIIb. The immunoreceptor tyrosine activation motif (ITAM)‐mediated signaling of B‐cell antigen receptors (left) or of activating FcγR (right) on innate immune cells such as macrophages and basophils is inhibited by IgG Fc‐mediated co‐cross‐linking of these activating receptors with the inhibitory FcγRIIb. This leads to phosphorylation of the FcγRIIb immunoreceptor tyros