After observing the rarity of infection on the tongue of cows, researchers at the Magainin Research Institute (PLYMOUTH Meeting, Maryland, USA) set about testing
whether a protective coating of naturally occurring antibiotics was responsible. Indeed, such a peptide - “lingual antimicrobial peptide“ (LAP) - has now been found to have in-vivo activity against
Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, and Candida spp (Science 1995; 267: 1645-48). LAP is a member of the beta-defensin class of antimicrobial peptides such as “tracheal
antimicrobial peptide“, isolated from ciliated epithelium of the upper airway of cows.
Complementary DNA cloning of LAP revealed a peptide 64 aminoacids long. LAP mRNA was found only on the dorsal surface of the tongue, and not in taste buds or subjacent lamina propria. It was also in surrounding areas of acute and chronic inflammation. Although LAP was not detected in third-trimester fetal cow tongue, it was abundant by the fourth month of life. Researchers surmise its production in infancy to be either developmentally regulated or the result of cumulative exposure to microbes.
The discovery of LAP adds to a growing list of peptide antibodies first described in the azurophilic granules of human and rabbit neutrophils (J Biol Chem 1978; 253: 2664-72). Several families of peptide antimicrobials are now recognized, including defensins, magainins, eceropins, and bacterial-permeability-increasing peptide.
David H Frankel
The LANCET 1995; 345: 850