IL17A and rheumatoid arthritis: Mice with collagen-induced arthritis (CIA) are a common animal model of rheumatoid arthritis, and CIA-susceptible mice with regularized microbiota have higher rates of arthritis than germ-free mice, higher concentrations of IL-17, higher proportions of CD8+ T and Th17 cells, and lower proportions of dendritic cells, B-cells, and Tregs, suggesting that the gut microbiota influences arthritis susceptibility (Liu et al. 2016).