C3 and rheumatoid arthritis: Notably, Chriswell ME et al.’s research established an association between a specific intestinal bacterium in the genus Subdoligranulum and various immunological phenomena, including local intestinal isolated lymphoid follicle formation, T cell and rheumatoid arthritis-associated autoantibody development, as well as paw swelling characterized by IgG, IgA, and C3 deposition in mice models (42).