New interleukins: are there any more?

Purpose of review It is now well established that cytokines play a critical role in the regulation of the immune system. Processes such as lymphoid development, differentiation, homeostasis, tolerance and memory are all regulated by cytokines that bind the type I family of cytokine receptors. Like the interferons, which bind receptors designated as the type II cytokine receptor family, type I cytokines also have essential functions in host defence. Recent findings Recently, a number of new interleukins and their receptors have been discovered and their role in mounting an appropriate immune response is currently being studied. In this review we will describe the new interleukin-12 family of cytokines, which now includes two other members: interleukins 23 and 27. We will also review the newly discovered interleukins 28 and 29, also known as interferon-As, which bind to the type II family of cytokine receptors, their structure and the structure of their receptors, their biological activities and modes of signalling. Summary These new molecules will certainly be the focus of active research in the immediate future. Their discovery opens the door to new therapeutic approaches to the treatment of various diseases ranging from infections from intracellular pathogens to viral infections.