MR1 and metabolic disease: While in both cases antigen presenting cells are likely to mediate MR1-dependent presentation and MAIT cell activation, it is conceivable that MAIT cell agonists within bacterial supernatants are complexed to other solutes and may require active phagocytosis for MR1 loading and presentation, which is impaired in PBMC from metabolic disease patients (33), and thereby confound the results.