Obesity-linked metabolic diseases, such as type 2 diabetes and cardiovascular disease, are associated with a state of low-grade inflammation. Recent research has elucidated many of the mediators and mechanisms that are involved in inflammation-associated metabolic disease. This Focus features articles that explore the interplay between metabolism and the immune system, explaining how inflammation drives type 2 diabetes, how fat-tissue-derived mediators are involved in inflammation and metabolic disease, and how T cell metabolism is linked to T cell fate.

Helper T cell heterogeneity was discovered two decades ago, initially with the designation of Th1 and Th2 cells, which are involved in immunity against intracellular and extracellular pathogens, respectively. Several years ago a third lineage was identified as the Th17 cells and several novel T cell subsets have since been found, including Treg and Tfh cells. The collection of articles presented in the May special issue and accompanying web focus summarize our understanding of the development and function of the T cell subsets in immunity and immune diseases.

The discovery of how to make monoclonal antibodies 35 years ago has revolutionized science and medicine, with more than 30 antibody-based products currently approved as biological agents for the treatment of many immune-mediated diseases and cancer. This Focus issue brings together specially commissioned articles on the basic biology of antibody receptors and on the important advances and further prospects for the development of more efficient, affordable and safer therapeutic antibodies.

Recent research in the area of neuroimmunology has focused on the role of immune cells, such as autoimmune T cells and microglial cells, in the initiation and progression of particular neurological diseases, such as multiple sclerosis and Alzheimer's disease. In addition, there have been important advances in our understanding of the effects of an inflammatory response in the brain owing to infection or injury. This Focus highlights these recent advances and their therapeutic implications.

Given the different biological functions of the known CD4+ T-cell subsets, an important current area of research is to determine the factors that control T helper (TH)-cell differentiation pathways in different conditions, with a view to understanding how these pathways might be manipulated for therapeutic benefit. This Focus describes the molecular pathways that govern the differentiation of TH1, TH2, TH17 and regulatory T cells.

Most infectious, allergic and inflammatory diseases in humans involve mucosal surfaces, including the gastrointestinal, reproductive and respiratory tracts. To maintain health, the mucosal immune system must provide protection against pathogens while being tolerant of commensal bacteria and harmless antigens. This Focus highlights the latest advances in our understanding of host-microbe interactions at mucosal sites and the consequences of immune dysregulation at these sites.

Millions of people worldwide suffer from respiratory diseases such as allergies, asthma and chronic obstructive pulmonary disease, and these diseases constitute a major public health burden. This Focus issue highlights the latest advances in our understanding of the immune bases of these diseases and outlines how this knowledge can be translated into more effective treatment strategies.

Immune tolerance is a built-in control mechanism to prevent the immune system from attacking self tissues, but when it goes awry autoimmune diseases can ensue. This Focus highlights the latest advances in our understanding of immune tolerance and anergy, and how this knowledge can be translated into effective immunotherapies.

Cytokines act as key communicators for immune cells and maintaining a delicate balance in the level of these communicators is vital for health. This special Focus issue highlights the latest advances in cytokine research and the application of these findings for clinical intervention.

Immunology is one of the few disciplines that straddle both basic sciences and applied medicine, and translating what we observe in the laboratory to the clinic is an increasingly important goal for many immunologists. This Focus highlights how basic research findings are being translated and applied to the treatment of cancer, and autoimmune and infectious diseases.

All the cells of the immune system are derived from precursor cells in the bone marrow. However, full development to become a T cell is completed in the thymus, not in the bone marrow as is the case for B cells. This Focus highlights our current understanding of several steps that are crucial for the complex process of early lymphocyte development.

Cells of the immune system communicate by cell–cell contact and through the production of soluble factors that bind cognate receptors expressed at the surface of target cells. This Focus on immune-cell communication highlights some of the diverse mechanisms of immune-cell communication.