Maternal Immunity Of Mannose-binding Lectin In Zebraifsh Danio Rerio

Complement system is a very important component of innate immunity. Thereare three activation pathways of complement system: the classical pathway,the alternative pathway and the lectin pathway. Lectin pathway has been considered tobe an ancient pathway, because both mannose-binding lectin (MBL) and MBL-associatedserine protease (MASP) have been found in the invertebrates. MBL is a patternrecognition molecule that can recognize antigen. MBL and MASP can combine to formMBL-MASP compounds, which can activate the lectin pathway. Thisstudy focuses on the maternal immunity of mannose-binding lectin in zebrafish.First, MBL lectin was purified from the homogenates of4?8cells stage embryos ofzebrafish, using affinity chromatography with a mannan-Sepharose. Second, MBL wasused to detect if it can bind to the microbes. The results showed that MBL exhibitedaffinity to both the gram-negative bacterium E. coli and the gram-positive bacterium S.aureus. Third, flow cytometric analysis was carried out to assess the effects of MBL onphagocytosis of bacteria by carp macrophages. The results showed that MBL was able topromote the phagocytosis of bacteria by carp macrophages. Fourth, we showed that theembryo homogenates was able to promote the phagocytosis, which was significantlyreduced by addition of MBL-antibody into the homogenates. Fitfh, microinjection ofpurified MBL into4-cell stage embryos was able to significantly enhance the survivalrate of the embryos challenged by live A. hydrophila (pathogenicto Danio rerio、、co-microinjection of MBL-antibody into4-cell stage embryos to blockMBL action and live A. hydrophila，the mortality of resulting embryos was significantlyincreased; whereas the antibody-induced embryonic death rate was remarkably reducedby the co-injection of MBL-antibody plus purified MBL. All these data suggested thatMBL was involved in the antimicrobial activity of developing embryos. Finally, weshowed the presence of MBL-associated serine protease (MASP) by Western-blotting. All these data suggest that MBL is involved in the maternal immunityof developing embryos in zebrafish, which probably plays a role via lectin pathway.