SYK (EC 2.7.10.2) is a non-receptor tyrosine kinase that contains two SRC homology 2 (SH2) domains and a kinase domain (Box 1) and is most highly expressed by haematopoietic cells. It is known to have a crucial role in adaptive immune receptor signaling. However, recent reports indicate that SYK also mediates other biological functions, including cellular adhesion, innate immune recognition, osteoclast maturation, platelet activation and vascular development. Recruitment of spleen tyrosine kinase (SYK) to plasma membrane receptors occurs through binding of the tandem SH2 domains of SYKto two phosphorylated tyrosine residues of the immunoreceptor tyrosine-based activation motifs (ITAMs) in the receptor complex. SYKis activated by C-type lectins and integrins, and activates new targets, including the CARD9–BCL-10–MALT1 pathway and the NLRP3 inflammasome[1].