CD4 and obesity due to melanocortin 4 receptor deficiency: The understanding on macrophage infiltration is still evolving while other pro-inflammatory immune cells including CD8+ cytotoxic T cells, CD4+ T helper (Th) 1 cells, neutrophils as well as B cells (particularly the B2 subtype that promote inflammation) have also been observed during the progression of obesity in animal models (18, 19).