Inflammatory arthritis is the term used to describe a heterogeneous group of conditions, including rheumatoid arthritis, juvenile idiopathic arthritis, spondylarthritis and psoriatic arthritis, and others, that are characterised by synovial inflammation affecting one or more joints. Progress in our understanding of the pathogenesis of these conditions has been parallelled by unprecedented therapeutic breakthroughs in the past two decades. This has been facilitated by a focus on early diagnosis and prompt treatment with (combinations of) conventional and biological antirheumatic drugs, notably in rheumatoid arthritis. The cellular and soluble components of inflammatory arthritis have been characterised in great detail, and the importance of the interplay between the immune system and stroma in the evolution from acute to chronic arthritis is now a widely accepted concept. Scientific advances have been spurred by the availability of new technologies to study gene and protein expression and analyse multiple surface markers on immune cells. This has resulted in the identification of new cellular subsets and better characterisation of the molecular pathways operational in chronic arthritis. The realisation that gene function can be modified by epigenetic factors (as captured in ‘the missing link’) has added a new layer of complexity to the study of biological processes including chronic joint inflammation. This might provide some link between the long known but incomplete genetic risk for these conditions that is clearly shaped by certain environmental, hormonal, and other factors.

Nevertheless we must equally admit that the picture still contains many holes and much remains to be done. We struggle to explain how arthritis evolves from the preclinical to the clinical stage, why it progresses to a chronic and sometimes destructive stage in a proportion of patients, and why the underlying pathological process in the joints seems to differ between patients with similar clinical phenotypes. With regards to therapeutics, we are starting to realise that immune modulatory drugs are not always sufficiently effective in suppressing chronic inflammatory arthritis, hence the continuous quest for novel treatments with different targets.

To shed some light on these outstanding questions, we have approached a selection of the finest clinical and translational scientists from industry and academia to write state-of-the-art chapters on their area of expertise. This has resulted in the present piece of work on Concepts of pathogenesis and emerging treatments for inflammatory arthritis , which covers the latest developments on a range of topics and illustrates the progress in the field. Above all we hope that this volume will inspire a new generation of scientists to join the effort to tackle the challenge of resolving the great mysteries of inflammatory arthritis.