Abstract
The human gut microbiota, which can weigh as much as 2 kg and harbor 100 trillion bacteria, is specific to each individual. In healthy adults, a balanced microbiota-a state known as eubiosis-can be altered by various factors such as diet and lifestyle. Microbiota imbalance-or dysbiosis-can have consequences for host health. Given that 80% of the human immune system is located in the gut, studies have investigated the role of the microbiota in immune system diseases, including joint and inflammatory pathologies such as rheumatoid arthritis. A better understanding of this pathology might enable the development of new treatments in the future. The microbiota includes all unicellular organisms in the digestive tract, including bacteria, viruses, fungi, and archaea. This complex ecosystem is unique to each individual. Associations between the human body and the microorganisms that it hosts can be considered mutualistic, symbiotic, or parasitic. These microorganisms are responsible for essential functions in maintaining health; the microbiota can even be considered another organ of the body. Microbiota composition varies considerably between early life and older age but remains relatively stable for most of a lifespan.