PTPRC and obesity due to melanocortin 4 receptor deficiency: To reinforce the conclusion that proliferation rather than monocyte migration plays critical role in ATM accumulation at the early stage of obesity, we analyzed the local expression of CCL2 (MCP-1) in adipose tissue, which is the pivotal chemoattractant for monocyte migration.16 Interestingly, employing intracellular staining, we found that CCL2 was mainly expressed by CD45−CD31− stromal cells in adipose tissue rather than CD45+ leukocytes or CD31+ endothelial cells.