Since the initial biochemical characterization of interleukin 1 (IL-1) and IL-2 a little more than a decade ago, the interleukins, which represent secreted regulatory proteins of the immune system, have emerged alongside neurotransmitters, endocrine hormones and growth factors as major regulators of cell and tissue function. Interleukins: Molecular Biology and Immunology is a concise series of chapters by different authors that focus on the structure and function of IL-1 to IL-8. The editor, Dr. Kishimoto, has directed attention to the areas of change in this field. In the past few years, the rapid movement from the identification of a new interleukin to the availability of recombinant interleukin has yielded a number of texts which have emphasized their role in haematopoiesis, inflammatory responses, and disease. Each interleukin is a multifunctional molecule with numerous biological activities, often overlapping those of several other interleukins. This book captures another theme, interleukin receptors and signal transduction mechanisms. While the primary structure of the interleukins does not reveal homology, their receptors show significant homology. Some receptor cDNAs encode membrane polypeptides that are responsible individually for expression of high-affinity ligand binding; others such as the IL-2, IL-3, and IL-6 receptors require cooperation of multiple subunits. A comparison of receptor structures suggests that there exist several receptor families, each of which appears to contain members derived from a common ancestral gene. The significance of the patterns of sequence conservation await the determination of the three-dimensional structure of at least one member of each family. It would appear likely that sequence homologies in the receptors may reflect a conservation in threedimensional structure, needed to retain highaffinity ligand binding since analysis of the se- quence of the interleukins themselves suggests that these molecules are all likely to have a four helix bundle structure.
The largest of the receptor families has been termed the hematopoietin receptor family. This type of receptor structure is characterised by specifically conserved cysteine residues that may