Endogenous Protein Protects Skin From E. coli

VIENNA — Healthy skin secretes an antimicrobial protein called psoriasin that is a potent Escherichia coli-killing compound, Regine Glaser, M.D., said at the annual meeting of the European Society for Dermatological Research.

Psoriasin appears to be the principal reason that cutaneous E. coli infection is rare despite the bowel bacterium's ubiquitous presence in daily life, according to Dr. Glaser of the department of dermatology at the University of Kiel (Germany).

Danish investigators first described psoriasin in psoriatic lesions in the late 1990s. Its function was unknown. But in recent studies, Dr. Glaser and her co-workers showed that psoriasin's main function appears to be to protect the skin from E. coli infection.

Reasoning that healthy skin's high degree of resistance to E. coli infection might be due to some innate defensive factor, Dr. Glaser looked for candidate compounds in human stratum corneum extracts. The 11-kd S-100 protein psoriasin emerged as the top candidate.

Moving on to in vivo work, Dr. Glaser used an antipsoriasin monoclonal antibody to show that high concentrations of psoriasin were produced selectively by keratinocytes located in the upper, more differentiated epidermal layers of the nose, the anogenital area, the armpits, and the sebaceous glands—all sites with high bacterial colonization rates. In contrast, psoriasin staining was patchy in skin on the extremities and other areas where bacterial colonization is less common.

Pretreating subjects' forearms with the antipsoriasin monoclonal antibody prior to application of E. coli to the skin led to markedly increased bacterial survival, said Dr. Glaser.

Psoriasin's antimicrobial spectrum showed a strong preference for E. coli. The compound's mechanism of killing E. coli appears to involve sequestration of zinc, which deprives the microorganism of an essential metal ion.

Dr. Glaser and her coinvestigators are exploring the potential utility of a psoriasin-based topical therapy.