TLR4 and obesity due to melanocortin 4 receptor deficiency: Indeed, elevated levels of bacterial endotoxin but also of wall compounds found in Gram-positive bacteria like lipoteichoic acid (LTA) and peptidoglycan and an activation of their receptor-dependent signaling pathways, e.g., signaling pathways regulated by Toll-like receptor 4 and 2 (TLR4 and TLR2), have been shown to be related to the development of obesity and metabolic alterations in humans14–16.