Researchers at National Jewish Medical and Research Center report in the New England Journal of Medicine that patients with atopic dermatitis, also known as eczema, are susceptible to bacterial infections of their skin because they fail to produce effective amounts of two antimicrobial peptides. The findings demonstrate the clinical significance of these peptides in humans, and suggest that a medication containing or inducing the peptides may one day be used to fight the infections that plague millions of atopic dermatitis patients.
"This study helps explain why 90 percent of atopic dermatitis patients are colonized by staphylococcus aureus and 30 percent develop active infections," said the study's senior author, Donal Leung, Head of Pediatric Allergy-Immunology at National Jewish Medical and Research Center, in Denver. "It is important to understand why people with this common skin disease are so susceptible to skin infections especially in light of recent widespread concerns that they can develop severe infections after receiving a smallpox vaccination. Interestingly, these antimicrobial peptides are also needed to combat viral infections and therefore could account for the susceptibility of atopic dermatitis patients to eczema vaccinatum and herpes simplex infections."
Atopic dermatitis is a common, chronic skin disease characterized by dry, itchy and easily irritated skin. It occurs most commonly in infants and young children, but can persist into adulthood. Severe cases can lead to sleep deprivation, chronic bacterial infections, and depression. Approximately one in nine people in the United States suffer from this diseases at some point. Along with other allergic diseases, its prevalence has grown significantly in recent years.
Immunologists recently identified peptides in the skin that help fight incipient infections. They rarely appear in normal skin, but are produced in reaction to skin inflammation. Since atopic dermatitis patients are so frequently plagued by bacterial infections, Dr. Leung and his colleagues decided to investigate the potential role of the antimicrobial peptides in those patients.
They evaluated the levels of two antimicrobial peptides, known as LL-37 and HBD-2, in eight patients with moderate to severe atopic dermatitis, 11 psoriasis patients, and six healthy individuals. Psoriasis is an inflammatory skin disease, whose patients rarely suffer skin infections. Microscopic examination of skin samples showed significant amounts of the peptides in the skin of psoriasis patients, but none to minor amounts in skin from atopic dermatitis patients, and none in the skin of healthy controls. Additional analysis indicated that most psoriasis patients had at least 10 times as much of the peptides in their skin as did atopic dermatitis patients. Many atopic dermatitis patients had no detectable amounts of the antimicrobial peptides in their skin.
When the researchers treated staphylococcus aureus colonies with the antimicrobial peptides, levels found in skin of psoriasis patients killed the bacterial. The researchers also found that two hormone-like proteins associated with the immune response and commonly secreted by atopic dermatitis patients' cells. "These findings indicate that atopic dermatitis patients have an impaired immune response that prevents them from producing adequate amounts of antimicrobial peptides in their skin," said Dr. Leung.