– Tyrosine-protein kinase Lyn is a member of the Src family of protein tyrosine kinases, which is mainly expressed in hematopoietic cells, in neural tissues liver, and adipose tissue. Tyrosine-protein kinase Lyn has many functions. Lyn kinase may downregulate the expression of stem cell growth factor receptor (KIT). Lyn kinase Acts as an effector of EpoR (erythropoietin receptor) in controlling KIT expression and may play a central role in erythroid differentiation during the switch between proliferation and maturation. Lyn kinase also acts as a positive regulator of cell movement while negatively regulating adhesion to stromal cells by inhibiting the ICAM-1-binding activity of beta-2 integrins. Lyn kinase relays suppressing signals from the chemokine receptor CXCR4 to beta-2 integrin LFA-1 in hematopoietic precursors. This kinase is involved in the induction of stress-activated protein kinase (SAPK), but not ERK or p38 MAPK, in response to genotoxic agents. In a word, Lyn kinase functions primarily as a negative regulator, but can also function as an activator, depending on the context. Tyrosine-protein kinase Lyn is Required for the initiation of the B-cell response, but also its down-regulation and termination. It also plays an important role in the regulation of B-cell differentiation, proliferation, survival, and apoptosis, and is important for immune self-tolerance. It has been reported that Lyn kinase plays a role in the inflammatory response to bacterial lipopolysaccharide. Lyn kinase Mediates the responses to cytokines and growth factors in hematopoietic progenitors, platelets, erythrocytes, and in mature myeloid cells, such as dendritic cells, neutrophils, and eosinophils.