Fig. 1

Age and gut microbiota enhance rheumatoid arthritis related autoimmune arthritis and pathological changes in the lung. a K/BxN mice aged 23 days (young) or 10–15 months old (middle-aged) were gavaged for 3 consecutive days with segmented filamentous bacteria (SFB) or left non-gavaged. At 20 days after the first gavage, ankle thickness was measured and is shown as mean ± SEM. Non-arthritic adult mice have a basal ankle thickness of ~2.8–2.9 mm (male mice have slightly greater ankle thickness than female mice) and thus ankle thicknesses of >3 mm are considered as indicative of arthritis (each dot indicates the mean value of the ankle thickness from both ankles of the same mouse). b Serum from young and middle-aged K/BxN mice was collected 20 days after the first SFB gavage. Anti-glucose-6-phosphate isomerase (Anti-GPI) autoantibody titers were determined by ELISA and are shown as mean ± SEM. c Spearman correlation between anti-GPI autoantibody titers and ankle thickness in SFB– and SFB+ young or middle-aged K/BxN mice (total of 17 mice from three independent experiments). d Representative images of lung histologic staining (H&E) from non-gavaged and day-20 SFB-gavaged young and middle-aged K/BxN mice. The combined and quantified data on areas of inducible bronchus-associated lymphoid tissue (iBALT)-like structures from 10 random, non-overlapped fields of each image are also shown (n = 3–8 mice in each group). e The SFB colonization levels of young and middle-aged K/BxN mice from the experiments as shown in a were checked at the indicated time points after SFB gavage; days indicates the number of days post first SFB gavage