TREM2 and obesity due to melanocortin 4 receptor deficiency: Given the essential role of ceramide in obesity noted in our previous report50 and that TREM2+ macrophages are enriched in obese adipose tissue, we reasoned that a high-fat diet (HFD) would promote ceramide generation and accelerate NcDase deficient TAM-impaired T-cell function and enhance tumor growth in vivo.