 In various hematopoietic cells, Lyn has emerged as a key enzyme involved in the regulation of cell activation.In these cells, a small amount of LYN is associated with cell surface receptor proteins, including the B cell antigen receptor (BCR), CD40, or CD19.The abbreviation Lyn is derived from Lck/Yes novel tyrosine kinase, Lck and Yes also being members of the Src kinase family.