Abstract
IL-5 is a cytokine released from T lymphocytes, mast cells, and eosinophils when infection or inflammation takes place. IL-5 is primarily and selectively engaged in eosinophil development. It works as a homodimer of a polypeptide with M. W. of 12, 500. It is heavily glycosylated to give the M. W. of 40 to 55 kDa. Its receptor consists of α and β chains. The IL-5 receptor a chain is 60 kDa glycoprotein that is the only IL-5 binding protein. The IL-5 receptor fi chain is a 130 kDa glycoprotein that does not bind any cytokines described. This β chain, however, is necessary to form the functional IL-5 receptor. In case of murine IL-5 receptor, α chain binds IL-5 with low affinity and becomes functional high affinity receptor when dimerized with β chain. In contrast, human IL-5 receptor a chain binds IL-5 with higher affinity than murine homologue. It is highly possible that soluble from of human IL-5 receptor α chain effciently block the IL-5 binding to its receptor. The IL-5 receptor β chain is also used as R chain for GM-CSF receptor and IL-3 receptor. These three cytokines which share fi chain are able to induce eosinophil hyperadherence to human microvascular endothelial cells. IL-5 and IL-3 also prime eosinophils, basophils and mast cells to produce leukotriene C4 in response to soluble agonists.
