IL17A and rheumatoid arthritis: An increased abundance of Prevotella copri was reported in treatment-naïve new-onset RA patients168,169 and in individuals at high risk for RA.170 Another study identified a strong link between three rare genera (Collinsella, Eggerthella and Faecalibacterium) and RA, among which Collinsella is associated with proinflammatory IL-17A production.171 In a Chinese cohort, RA patients displayed an over-representation of Lactobacillus salivarius and reduced levels of Haemophilus spp.