A first aspect of the invention relates to the bacterial species Roseburia hominis for use in: regulating the immune system of a subject treating an immune disorder; treating an intestinal disorder; improving intestinal microbiota; regulating the innate immune system of a subject; regulating the adaptive immune system of a subject; regulating appetite in a subject; promoting Tregs and immune tolerance; promoting gut health in a subject; and/or maintaining immune homeostasis in a subject. Further aspects of the invention relate to compositions comprising Roseburia hominis.