Building further on his experience with Lyme arthritis, Steere is now conducting studies of infection-induced autoimmunity in patients with rheumatoid arthritis. With his colleagues Annalisa Pianta and Elise Drouin, he has reported a link between immune responses to a commensal microorganism in the gut microbiome, Prevotella copri, and two novel autoantigens (human proteins) that are highly expressed in joints of rheumatoid arthritis patients. These studies demonstrated molecular mimicry between these microbial and human proteins, and in some cases, Prevotella DNA was found in patients’ inflamed joints, suggesting that the organism itself or components of it may sometimes reach the joints of rheumatoid arthritis patients. These findings, which have implications for the diagnosis and treatment of the disease in the future, were highlighted in recent articles in Arthritis and Rheumatology and the Journal of Clinical Investigation.