CD1D and obesity due to melanocortin 4 receptor deficiency: One particular type of immune cells, invariant Natural Killer T-cells (iNKT cells), has attracted attention in obesity for several reasons: (i) in healthy AT they can make up to 20% of the immune cell population [14,15], (ii) AT-resident iNKT cell numbers decline in obesity and various mouse models indicate that they support optimal AT function [14,16], (iii) iNKT cells can be activated by lipid antigens presented in the context of CD1d by adipocytes [16–18].