Abstract
It is well established that innate mechanisms play an important role in the immunity of fish. Antimicrobial peptides have been isolated and characterized from several species of teleosts. Here, we report the isolation of an antimicrobial compound from the blood of bacterially challenged sea lamprey, Petromyzon marinus. An acetic acid extract from the blood cells of challenged fish was subjected to solid-phase extraction, cation-exchange chromatography, gel-filtration chromatography, and reverse-phase high-performance liquid chromatography, with the purified fractions assayed for antimicrobial activity. Surprisingly, antimicrobial activity in these fractions originated from squalamine, an aminosterol previously identified in the dogfish shark, Squalus acanthias. Further chromatographic and mass spectrometric analyses confirmed the identity of squalamine, an antimicrobial and antiangiogenic agent, in the active fraction from the sea lamprey blood cells. Immunocytochemical analysis localized squalamine to the plasma membrane of white blood cells. Therefore, we postulate that squalamine has an important role in the innate immunity that defends the lamprey against microbial invasion. The full biochemical and immunological roles of squalamine in the white blood cell membrane remain to be investigated.
Highlights
It is well established that innate mechanisms play an important role in the immunity of fish
We discovered the antimicrobial substance squalamine in the lamprey blood cells
Immunocytochemical localization of squalamine to the plasma membrane of the white blood cells indicates a possible function as an immune effector
Summary
It is well established that innate mechanisms play an important role in the immunity of fish. Li. Identification of squalamine in the plasma membrane of white blood cells in the sea lamprey, Petromyzon marinus. There have been numerous reports of effector molecules associated with innate immunity and antimicrobial peptides in several well-known fish species. These molecules include pardaxin from the Moses sole Pardachirus marmoratus [5], chrysophsin from the red sea bream Chrysophrys major [6], pleurocidin from the winter flounder Pleuronectes americanus [7], parasin I from the catfish Parasilurus asotus [8], misgurin from the loach Misgurnus anguillicaudatus [9], hipposin from the Atlantic halibut Hippoglossus hippoglossus [10], and bass hepsidin, piscidins, and moronecidin from the hybrid striped bass [11,12,13]. This article is available online at http://www.jlr.org
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