Syk is a cytoplasmic72 kD non-receptor tyrosine kinase thatis widely expressed in hematopoietic cells. The Syk kinase associates with a number of proteins including c-Src, Lck, Lyn, Fyn, Vav1, STAT3, SHP1, Grb2, and LAT to couple immunoreceptors to downstream signaling events mediating cellular proliferation, differentiation, and phagocytosis. Syk is modified by phosphorylation on multiple tyrosine sites. The SYK-01 monoclonal antibody (raised against amino acids 5-360 of human Syk) recognizes human, mouse, and rat and Syk and has been shown to be useful for Western blotting, immunoprecipitation, and immunohistochemistry.