Submitted on June 26, 2007
Revised on August 27, 2007
Accepted on August 28, 2007
Identification of squalamine in the plasma membrane of white blood cells in the sea lamprey, Petromyzon marinus
Sang-Seon Yun and Weiming Li
Department of Fisheries and Wildlife, Michigan State University, East Lansing, MI 48824
Corresponding Author: liweim{at}msu.edu
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 reversed 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 spectrometry analyses confirmed the identity of squalamine, an anti-microbial and anti-angiogenic agent in the active fraction from the sea lamprey blood cells. Immunocytochemical analysis localized squalamine to the plasma membrane of white blood cells. We therefore 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.
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