Jak2, also known as Janus Kinase 2, is a non-receptor tyrosine kinase enzyme that plays a crucial role in cellular signaling pathways. It belongs to the Janus kinase (JAK) family of enzymes, which are involved in the transmission of signals from cell surface receptors to the nucleus. Jak2 is activated by various cytokines, including erythropoietin (EPO), thrombopoietin (TPO), and growth hormone (GH), among others. Upon activation, Jak2 phosphorylates specific tyrosine residues on the receptor and on downstream signaling molecules, initiating a cascade of cellular responses. Jak2 is essential for normal hematopoiesis, as it regulates the proliferation, differentiation, and survival of hematopoietic stem cells and progenitor cells. Mutations in Jak2 can lead to hematological disorders, such as polycythemia vera (PV), essential thrombocythemia (ET), and primary myelofibrosis (PMF). Jak2 also plays a role in immune responses by modulating the activity of immune cells, including T cells, B cells, and natural killer (NK) cells. It contributes to the regulation of cytokine production and the activation of immune effector functions.