JAK, or Janus kinase, is a type of enzyme that plays a crucial role in cell signaling. It helps transmit signals from various growth factors and cytokines, which are important for immune responses and cell growth. JAKs are involved in several biological processes, including inflammation and hematopoiesis, the formation of blood cells. There are four main types of JAK enzymes: JAK1, JAK2, JAK3, and TYK2. Each of these enzymes has specific functions and is associated with different diseases. Inhibitors targeting JAK enzymes are used in treatments for conditions like rheumatoid arthritis and psoriasis, helping to reduce inflammation and improve patient outcomes.