Microbiota in T-cell homeostasis and inflammatory diseases

The etiology of disease pathogenesis can be largely explained by genetic variations and several types of environmental factors. In genetically disease-susceptible individuals, subsequent environmental triggers may induce disease development. The human body is colonized by complex commensal microbes that have co-evolved with the host immune system. With the adaptation to modern lifestyles, its composition has changed depending on host genetics, changes in diet, overuse of antibiotics against infection and elimination of natural enemies through the strengthening of sanitation. In particular, commensal microbiota is necessary in the development, induction and function of T cells to maintain host immune homeostasis. Alterations in the compositional diversity and abundance levels of microbiota, known as dysbiosis, can trigger several types of autoimmune and inflammatory diseases through the imbalance of T-cell subpopulations, such as Th1, Th2, Th17 and Treg cells. Recently, emerging evidence has identified that dysbiosis is involved in the progression of rheumatoid arthritis, type 1 and 2 diabetic mellitus, and asthma, together with dysregulated T-cell subpopulations. In this review, we will focus on understanding the complicated microbiota-T-cell axis between homeostatic and pathogenic conditions and elucidate important insights for the development of novel targets for disease therapy. Imbalances in the body's community of microbes can trigger diseases such as rheumatoid arthritis, diabetes, and asthma. The factors that disrupt the immune system and cause autoimmune diseases are poorly understood. Wan-Uk Kim and Naeun Lee at The Catholic University of Korea, Seoul, Korea have reviewed the evidence that the body's community of microbes, the microbiota, affects immune system development and T cell differentiation. T cells, white blood cells that distinguish healthy from diseased cells, are important components of the immune system. In healthy individuals the many types of T cells are produced in balanced quantities. Kim and Lee report that patients with rheumatoid arthritis, diabetes, and asthma show imbalances in both T cell populations and in their gut, lung, or oral microbiota. Understanding how different microbiota profiles are related to immune development could lead to new treatments.