Identification and functional characterization of fish-egg lectin in zebrafish

•A fish-egg lectin zFEL is identified in zebrafish.•zFEL is present in eggs.•zFEL interacted with Gram-negative and Gram-positive bacteria.•zFEL enhanced phagocytosis of microbes by macrophages.•Injection of purified zFEL into embryos promoted their resistance to Aeromonas hydrophila.

Fish-egg lectins (FELs) are identified in several species of fishes, but their activity and mode of action remain largely unknown in early life stages. Here we showed that zebrafish FEL (zFEL) was a maternal factor, which was capable of interacting with Gram-negative and Gram-positive bacteria and enhancing the phagocytosis of the bacteria by macrophages. Interestingly, microinjection of purified native zFEL into the embryos (resulting in the increase of zFEL in the embryos) markedly promoted the resistance of the embryos to the pathogenic Aeromonas hydrophila. Taken together, zFEL appears a maternal immune-relevant molecule capable of defending the developing embryos/larvae from pathogenic attacks.