INS and obesity due to melanocortin 4 receptor deficiency: It has been suggested that IL-15 and aberrant leptin secretion with obesity might instigate an adipose-specific NK-cell expansion and activation in response to high-fat diet overfeeding, stimulating NK-cell IFN-γ, TNF-α, and MCP-1 production, negatively impacting whole-body insulin sensitivity (96–98).