An appetite-controlling hormone, leptin, has been found to enhance the immune system, according to a study at the Michigan State University.
Scientists already know that a number of factors can affect the body's immune system such as poor diet, certain steroids, and chronic stress.
However, this is the first time leptin's effect on the immune system has been demonstrated.
'These two studies, while not directly related, show that the neuroendocrine system plays a big role in both the immune system and obesity,' said Pamela Fraker, MSU professor of biochemistry and molecular biology and lead author.
The researchers found that leptin, a hormone produced by fat cells, supports white blood cell production in the body, enhancing immune function.
It is already known that leptin helps control how much a person eats as well as how quickly the body burns energy.
'Many investigators have been trying to unlock the key to obesity for years. The more fat a person has, the more leptin there is in the bloodstream. In obese people, it seems that the body becomes leptin-resistant -- the signals get jammed. So giving obese people leptin doesn't help them lose weight,' said Fraker
The researchers examined ob/ob mice (genetically programmed to have non-functional leptin) and db/db mice (genetically programmed to have non-functional leptin receptors), giving them supplemental leptin to study its effects.
While causing the mice to eat less, the big surprise was leptin's effect on the immune system.
The mice that received leptin had double the number of B cells, a type of white blood cell produced in bone marrow that fights infection by making antibodies.
'This is a brand new role for leptin. It appears that most obese people may be somewhat immunosuppressed. This finding shows us that the body's resistance to leptin plays a role in that, too,' Fraker said.
The study is reported in this week's online edition of the Proceedings of the National Academy of Sciences.