With the progression of CIA, the abundance of the operational taxonomic units (OTUs) affiliated with the families Bacteroidaceae, Lachnospiraceae, and S24-7 was markedly upregulated in CIA-susceptible mice; if germ-free mice were administered the microbiota from either CIA-susceptible or CIA-resistant mice, the former group presented a higher incidence of arthritis with increased IL-17 levels and CD8+ T cell and Th17 lymphocyte proportions but decreased dendritic cells (DCs), B cells, and Treg cells in the spleen than the latter group [85]. Here, IL17A is linked to Arthritis.