Figure 3.

Model for the initial phosphorylation of the ITAMs within the Igα/Igβ sheath. In principle, two models for the initiation of BCR signalling are discussed: the allosteric activation of cytoplasmic protein–tyrosine kinases upon antigen binding (a), and the activation of cytoplasmic protein–tyrosine kinases upon clustering of two or more BCRs on the membrane (b). However, the kinases leading to the initial phosphorylation event could be preassociated to the cytoplasmic tails of Igα/Igβ (Pre-association model), or the BCRs, as a result of the clustering, are translocated to specialized membrane locations (signalling domain or lipid raft model).