Fig. 2

Role of Bruton’s tyrosine kinase downstream of the B cell receptor. Signaling cascade showing important events downstream of B cell receptor (BCR). Antigen engagement by the BCR results in the formation of a micro-signalosome whereby BTK activates four families of non-receptor protein tyrosine kinases that transduce key signaling events including phospholipase Cγ, mitogen-activated protein kinase (MAPK) activation, nuclear factor kappa-light-chain-enhancer of activated B cells (NF-кB) pathway components and activation of the serine/threonine kinase AKT (PKB). In addition, BTK mediated signaling events are regulated by various phosphatases that can be recruited to the cell membrane, following crosslinking of inhibitory receptors, e.g., FcγRIIB that is exclusively expressed on B cells and signals upon immune complex binding. See text for details