Natural Antibiotics Exist in Mammals' Skin
Excerpt By Amy Norton, Reuters Health

NEW YORK (Reuters Health) - Particular infection-fighting proteins act as natural antibiotics in the skin of mice, according to US scientists. It is the first evidence in mammals that such proteins, known as antimicrobial peptides, can perform like antibiotic drugs.

Since humans also have these types of proteins, the researchers say their findings suggest people can churn out their own antibiotics in the face of a germ invasion.

The study looked at the role of cathelicidins in the innate immune defenses of mice. Cathelicidins, or caths, are small pieces of protein that dwell in certain cells in mammals, including humans. While caths have been known to aid in the body's defenses--such as helping wound healing--it has been unclear whether they can kill infectious bugs.

In the November 22nd issue of Nature, Dr. Richard L. Gallo and his colleagues report that caths are indeed a type of natural antibiotic.

Gallo's team studied a mouse cathelicidin called CRAMP, which has a human counterpart called LL-37. This suggests that the human cath is also an innate antibiotic, according to Gallo, a researcher at the University of California, San Diego and the Veterans Affairs San Diego Healthcare System.

This is important for several reasons, Gallo told Reuters Health in an interview.

For one, he explained, ``this makes us wonder if people who get infections easily don't have proper function in their (caths).'' Further research, according to Gallo, should look into that question.

In addition, if humans harbor their own antibiotics, these natural-born germ killers could be used as models for drug development. Gallo pointed out that, unlike man-made antibiotics, caths have persisted throughout time without a wide range of bacteria becoming resistant to them.

In their study, Gallo's team created mice lacking the gene for CRAMP, then compared their susceptibility to skin infection from streptococcus bacteria with that of normal mice. They found that the CRAMP-deficient mice developed more severe infections than the normal animals did.

Similarly, in a second round of experiments, mice that were infected with mutant strep bacteria resistant to CRAMP had longer-lasting, more extensive skin infections than those infected with normal strep.

Caths are located in various tissues other than skin, including the lungs and intestines, and in white blood cells called neutrophils. According to Gallo, they jump into action when necessary, increasing their levels in tissue under assault.

Unlike antibiotic drugs, which are notoriously overused, he noted, ``the body doles out caths only when needed.''

SOURCE: Nature 2001;414:454-457.

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