Vitamin D has been credited with a role in antimicrobial peptide (AMP) production and in the body’s overall immune response, but scientists at the University of California, San Diego School of Medicine say a hormone previously associated only with maintaining calcium homeostasis and bone health is also critical, boosting AMP expression when dietary vitamin D levels are inadequate.
In cultured cell studies, fat-soluble vitamin D provides strong immunological benefits, but in repeated studies with humans and animal models, results have been inconsistent: People with low levels of dietary vitamin D do not suffer more infections. For reasons unknown, their immune response generally remains strong, undermining the touted immunological strength of vitamin D.
Working with a mouse model and cultured human cells, Richard L. Gallo, MD, PhD, professor of medicine and chief of UCSD’s division of dermatology and the dermatology section of the Veterans Affairs San Diego Healthcare System, and colleagues discovered that when levels of dietary vitamin D are low, production of parathyroid hormone (PTH)—which normally helps modulate calcium levels in blood—is ramped up. More PTH—or a related peptide called PHTrP—spurs increased expression of AMPs, such as cathelicidin, which kill a broad spectrum of harmful bacteria, fungi and viruses.
“No one suspected a role for PTH or the PTH-related peptide in immunity,” said Dr. Gallo. “This may help resolve some of the controversy surrounding vitamin D. It fills in the blanks.”
Dr. Gallo said PTH’s newly revealed immunological role provides a connection between the body’s endocrine system and its ability to fight invasive, health-harming pathogens.
The finding, published in the May 23, 2012 online issue of Science Translational Medicine, more fully explains how the immune system functions in different situations and presents a new avenue for treating infections, perhaps as an alternative to current antibiotic therapies.
While much more work remains to be done, including human studies, it’s possible that PTH or PTHrP might eventually become an effective antibiotic treatment without the risk of antibiotic resistance in targeted microbes. One challenge would be how to specifically limit treatment to the targeted infection. “Maybe that could be done by developing the therapy as a cream,” said Dr. Gallo.