Barely a day goes past without the publication of another paper featuring cytokines. So rather than become overwhelmed by the ever-increasing literature, we thought we should celebrate this fact and help our readers to keep up to date by featuring a collection of specially commissioned articles that highlight the latest advances in cytokine biology and cytokine-targeted therapies.

On page 429, Iain McInnes and Georg Schett introduce us to the complexity of cytokine networks in rheumatoid joints, where a dynamic and hierarchical mixture of cytokines is responsible for the debilitating features of this disease. Besides the well known role for tumour-necrosis factor in the pathogenesis of rheumatoid arthritis and the efficacy of biological agents that target this cytokine, how many other cytokines might prove to be useful therapeutic targets? On page 443, Yuri Rubtsov and Alexander Rudensky illustrate how the dysregulation of just a single cytokine — transforming growth factor-β — can have a devastating effect, owing to the unrestrained activities of self-reactive T cells. The control of immune cells is also the key message of the Review on page 454, which describes how SOCS (suppressor of cytokine signalling) proteins are involved in the cross-regulation of cytokine signalling pathways to ensure proper immune-cell function.

In our Research highlights section, we follow the latest advances on the newly identified subset of T helper cells that produce interleukin-17 (TH17 cells). Studies in mouse models place TH17 cells as crucial effectors in several inflammatory diseases. Now, with the detailed characterization of these cells in humans (pages 413 and 419), our interest in this field looks set to soar.

Finally, we acknowledge support from the Federation of Clinical Immunology Societies (FOCIS) and Beckman Coulter for this Focus issue and the accompanying Web Focus (http://www.nature.com/nri/focus/cytokines).