The underlying theory of blood type diets is that people with different blood types digest lectins differently, and that if people eat food that is not compatible with their blood type, they will experience many health problems.
Leptin is a potent stimulator of the immune system. Leptin receptors on monocytes cause the release intracellularly of STAT3 which cause the monocytes to release IL-6, IL-12 and TNF alpha. The IL-6 goes to the liver and increases production of CRP.
Leptin was the first fat cell-derived hormone to be discovered. Subsequent studies in 1995 confirmed that the db gene encodes the leptin receptor, and that it is expressed in the hypothalamus, a region of the brain known to regulate the sensation of hunger and body weight.