Expression And Functional Characterization Of Mannose-binding Lectin In Zebrafish

The lectin pathway involves recognition of pathogen-associated molecularpatterns by mannose-binding lectin (MBL), and the subsequent activation ofassociated enzymes, termed MBL-associated serine proteases (MASPs).In this study, we demonstrate that the transcript of MBL gene is present in theearly embryo of zebrafish, and MBL protein is present in zebrafish embryo. We alsoshow that recombinant zebrafish MBL was able to bind the Gram-negative bacteriumEscherichia coli and the Gram-positive bacterium Staphylococcus aureus, and rMBLwas able to promote the phagocytosis of E. coli and S. aureus by macrophages,indicating that like mammalian MBL, zebrafish MBL performs a dual function in bothpattern recognition and opsonization. Importantly, we show that microinjection ofanti-MBL antibody into the early developing embryos resulted in a significantlyincreased mortality in the resistance of recipient embryos to Aeromonas hydrophila;and injection of rMBL into the embryos (resulting in increase in MBL in the embryo)markedly promoted their resistance to A. hydrophila, and this promoted bacterialresistance was significantly reduced by the co-injection of anti-MBL antibody plusrMBL but not by the injection of anti-actin antibody plus rMBL. These suggest thatthe lectin pathway may be already functional in the early embryos in zebrafish beforetheir immune system is fully matured, protecting the developing embryos frommicrobial infection. This work provides a new angle to understand the immune role ofthe lectin pathway in early development of animals.