TLR4 and obesity due to melanocortin 4 receptor deficiency: The in vivo pathophysiological importance of TLR4 in obesity-induced inflammation and insulin resistance was investigated by using mice deficient in TLR4 signaling owing to invalidation of TLR4 (TLR4−/− mice) or to a loss-of-function mutation in the Tlr4 gene (C3H/HeJ and C57BL/10ScN) (Table 1).