CHAMPAIGN, Ill. -- Scientists have located -- and produced a vivid picture
of -- specific cells that contain receptors for a hormone-like substance
made by the immune system and associated with declines in growth-hormone
production in animals with bacterial infections.
The findings included two surprises and may help scientists understand how the immune system harnesses other physiological systems to regulate animal growth and disease. First, the receptors were found on cells in the pituitary gland, and, second, they were on somatotrope cells, which make growth hormone. Previous theory held that they were on corticotrope cells, makers of stress hormones.
The research, directed by Keith Kelley, a University of Illinois animal scientist and immunologist, led to a color snapshot of a direct link between the body's immune and endocrine systems. The work was featured on the cover and inside the September issue of the journal Endocrinology.
Specifically, researchers identified two types of receptors for interleukin-1 (IL-1), a molecule produced by the body's immune system during a bacterial infection, on the somatotrope cells in the pars anterior (outside sections) of the pituitary gland. The research, funded by the National Institutes of Health, was done using monoclonal antibodies as a stain to zero in on the morphology of cells in mice.
"This work shows us a marriage of the endocrine and immune systems," Kelley said. "These data give us a new set of glasses -- a new way of looking at the world that has always assumed that such interaction had to occur in the brain. The findings suggest that growth-hormone synthesizing cells in the pituitary also have the eyes that can sense the presence of disease-causing bacterium."
When a bacterium enters the body, it is taken in by macrophages, which are cells scattered throughout the body that ingest foreign cells. The bacterium causes the macrophages to produce IL-1, a message-carrying polypeptide with fever-inducing properties. It had been assumed, Kelley said, that the message of IL-1 was received in the hypothalamus, where response orders for growth-hormone production would originate and be controlled.
It also is known that the pituitary gland, located at the base of the brain, is essential for the body's resistance to bacteria. But the possibility that the pituitary gland may actually receive the message of illness and directly issue response orders, offers a new window for research, Kelley said. The mission now, he added, is to determine what the receptors actually do.
"We've discovered what physiologists learned 100 years ago," Kelley said. "There are physiological feedback systems, but this is in the context of not the heart talking to the kidney, not the brain talking to the heart, but in the context of the immune system talking with the endocrine system."
Co-authors of the paper were Kelley, Richard A. French and James F. Zachary of the U. of I. College of Veterinary Medicine, and researchers from INRA-INSERM (the equivalent of the USDA and NIH in France) and Hoffman LaRoche, an international pharmaceutical company.