Both the original Traj18−/− (10) and the Cd1d−/− (12–14) mice have been used by many different research groups to study the role of iNKT cells and/or type II NKT cells in obesity-related pathologies in high fat diet (HFD)-induced obesity models. This evidence concerns the gene TRAJ18 and obesity due to melanocortin 4 receptor deficiency.