Antimicrobial peptides exist in the epithelial tissues and blood cells of many vertebrates, but no antibiotic has been isolated from the mast cells of any animal. In November 15 Nature Umaporn Silphaduang and Edward Noga from North Carolina State University, Raleigh, US identified a family of peptide antibiotics that reside in the mast cells of fish. These 'piscidins' suggests that mast cells may participate in direct killing of microbial invaders.

Silphaduang & Noga used tissues derived from aquacultured, hybrid striped bass (Morone saxatilis x M. chrysops) and immunolocalized piscidins to mast cells in gill, skin, gut and blood vessels lining the viscera. In addition, they found that not all mast cells were positive for piscidins, indicating that piscidin-negative mast cells may be at a different stage of development or may have differentiated independently of the piscidin-positive lineage (Nature 2001, 414:268-269).

Peptide antibiotics may also be present in the mast cells of other vertebrates. "Our discovery indicates that these cells may be critical in fighting many infectious diseases", concluded the authors.