For example, butyric acid in SCFAs can inhibit the proliferation of Th1 cells (Guilloteau et al., 2010), the main cytokines secreted by Th1 cells are TNF-α, IFN-γ, and IL-2, so butyric acid can inhibit the secretion of pro-inflammatory factors and play an immunomodulatory role; or lipopolysaccharide in the flora can promote the secretion of pro-inflammatory factors and induce chronic systemic inflammation (Nicholson et al., 2012). Here, TNF is linked to inflammatory response.