TLR4 and obesity due to melanocortin 4 receptor deficiency: Several experimental models, including the use of bone marrow transplants (BMTs) to generate TLR4 chimeras where TLR4 is either present or absent from the whole body or from the BM-derived cells, have been developed to explore the cell-specific effects of TLR4 in obesity [21,29,31], but these studies have generated conflicting results.