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.
