Interleukin-5, eosinophilic diseases and therapeutic intervention

Interleukin 5 (IL-5) is the key cytokine in an eosinophil's life span: it supports eosinophilopoiesis and eosinophil differentiation, contributes to eosinophil migration, tissue localisation and function, and prevents eosinophil apoptosis. Given the likely role of eosinophils in chronic inflammatory diseases, a lot of research over the past decade was aimed at antagonising IL-5 function. It appears from recent studies that, although this can easily be achieved in vitro, blocking IL-5 function in vivo is much more difficult than originally anticipated. Here, we review the current status of IL-5 and IL-5 receptor research, with emphasis on strategies to interfere with IL-5 function.