Hormone plays surprise role in fighting skin infections

Vitamin D has been credited with a role in their 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.

23 May 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.

The immunological benefits of vitamin D are controversial. In cultured cell studies, the fat-soluble vitamin 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, Gallo and colleagues discovered why - when levels of dietary vitamin D are low (it's naturally present in very few foods), 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 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. ''This may help resolve some of the controversy surrounding vitamin D. It fills in the blanks.''