IL17A and inflammatory bowel disease: For example, in inflammatory bowel diseases, a higher proportion of Bacteroides, Bacteroidales, and Enterobacteriaceae, and lower proportion of Firmicutes, such as Faecalibacterium prausnitzii, induces reduction of SCFAs as metabolites from the bacteria, which exacerbate colitis, characterized by an increase in tumor necrosis factor alpha (TNF-α), interferon gamma (IFN-γ) and interleukin 17A (IL-17A), with differentiation of T helper cell 1 (Th1), Th2, and Th17 from naïve T cells (33).