STAT3 and obesity due to melanocortin 4 receptor deficiency: One study also looked at the synergic effect of infection and obesity and found that Helicobacter felis-infected mice fed on HFD accelerated gastric carcinogenesis through elevated immune response induced by adipose-derived IL-6 and leptin, and heightened pro-survival gene expression in gastric tissue through STAT3 signaling [31].