Type 1 diabetes is an autoimmune disease caused by the destruction of pancreatic beta cells by effector autoreactive T cells. Our studies in mouse models of type 1 diabetes have highlighted the regulatory function of iNKT cells in the prevention of this disease.  Recent advances in understanding the etiology of obesity and type 2 diabetes have established the involvement of the immune system. Obesity and T2D are associated with low-grade inflammation, activation of immune cells and alteration in gut microbiota. Since MAIT cells recognize bacterial ligands, we have undertaken the analysis of these cells in obese and T2D patients. Our data reveal major alterations of MAIT cells in the blood and adipose tissue of obese and T2D patients as compared to healthy lean control individuals, suggesting their potential role in these pathologies. Further studies are underway to analyze iNKT and MAIT cells in type 1 diabetic patients as well as to investigate the role of MAIT cells in mouse models of type 1 and type 2 diabete