IL17A and obesity due to melanocortin 4 receptor deficiency: In most rheumatic diseases, IFN-γ and TNF produced by circulating MAIT cells decrease, while IL-17 produced by MAIT cells increases in blood and tissues (Figure 2), suggesting that MAIT cell proinflammatory IL-17 is biased in rheumatology similar to that in obesity and chronic liver disease (67–69).