AHR and rheumatoid arthritis: Butyrate is a short-chain fatty acid that has been previously described to have anti-inflammatory effects in both RA and CIA, where it suppresses the severity of disease through several mechanisms, including: regulating differentiation of regulatory B (Bregs) and T cells (Tregs); indirectly amplifying aryl-hydrocarbon receptor activation in Bregs; reducing proinflammatory cytokine and anti-CII antibody production; increasing IL-10 production; and inhibiting osteoclastogenesis [31–36].