Antimicrobial peptides (AMPs) are increasingly recognized as a critical component of the host's defense against infection. Several types of AMPs have been recently identified from mucosal tissues or immune cells of a number of teleosts. Among these are the piscidins, which are 22 residue, α-helical AMPs that were originally isolated from mast cells of hybrid striped bass Morone saxatilis male × Morone chrysops female. Using an antibody specific for the conserved N-terminal amino acid sequence of piscidin 1, we used immunohistochemistry to probe skin, gill, and gastrointestinal tract of 39 teleosts representing 7 different orders. Nine fish species were piscidin-positive, with all of these species being in the Perciformes, the largest and most evolutionarily advanced order of teleosts. Piscidin-positive cells were identified in species belonging to the families Moronidae, Serranidae, Sciaenidae, Siganidae and Belontidae. Immunopositive cells were usually most consistent with mast cells, although in some species, the granule appearance and tinctorial properties diverged somewhat from those of a typical piscine mast cell. In addition, rodlet cells were piscidin-positive in one member of the family Cichlidae; to our knowledge, it is the first time that a host-associated chemical biomarker has been identified in rodlet cells. Our data suggest that piscidins are present in many evolutionarily advanced teleosts. Piscidin-immunoreactive cells were most common at sites of pathogen entry, including the skin, gill and gastrointestinal tract. These results strongly suggest that piscidins are a widespread and important component of many fishes' defense against disease.
KEY WORDS: Piscidins · Mast cells · Rodlet cells · Innate immunity · Pisces
Resale or republication not permitted without written consent of the publisherDis Aquat Org 72: [241][242][243][244][245][246][247][248][249][250][251][252] 2006 tissues of hybrid striped bass; the parental stocks of hybrid striped bass (white bass Morone chrysops and striped bass M. saxatilis) are in the family Moronidae, and similar appearing cells were positive in members of the family Sciaenidae (spot Leistomus xanthurus and Atlantic croaker Micropogonias undulatus). This prompted us to hypothesize that piscidins are present in other teleosts. To answer this question, we immunochemically examined tissues from 7 different orders of teleosts. Presumptively healthy, subadult to adult, farm-raised fish, as well as wild-caught individuals, were examined in the present study.
MATERIALS AND METHODSPeptide synthesis. Piscidin 1 (both the entire peptide and an 11-mer fragment) and Magainin 2 peptides were synthesized using Fmoc chemistry on a Rainin Symphony instrument that provides on-instrument cleavage of the peptide from the resin. After synthesis, peptides were purified via analytical reverse phase HPLC using a YMC C-18 column (4 × 50 mm, 3 µm particle size, 120 Å pore size support) using an acetonitrile gradient that was eluted at 1 ml min -1 where Buffer A was 0.05% trif...