Cross-species opsonic activity of zebrafish fish-egg lectin on mouse macrophages

Zebrafish Fish-egg lectin (zFEL) has been identified and proved to be a maternal factor with antibacterial and opsonic ability in fishes. In this study, we found that zFEL was capable of enhancing the phagocytosis of the bacteria by macrophages of mouse (RAW264.7 and mouse peritoneal macrophages), suggesting a cross-species function of zFEL in higher animals. Further studies showed that zFEL can active the antigen presentation ability by up-regulating the expression of CD80, CD86 and MHC II. Meanwhile, zFEL also promoted the polarization of macrophages to M1-type, which was confirmed by the increase of cytokines TNF-α and IL-6. The expression of p38 gene was up-regulated in macrophages preincubated with zFEL. Taken together, zFEL appears opsonic function in mammal macrophages and has potential application in immunomodulation.

Antibacterial functions of a novel fish-egg lectin from spotted knifejaw (Oplegnathus punctatus) during host defense immune responses

Fish-egg lectins (FELs) have been identified in several teleost species and have been proved to play important roles in innate immune system against pathogen infection. In this study a novel fish-egg lectin (OppFEL) was identified from spotted knifejaw (Oplegnathus punctatus), and the expression patterns against bacterial infection was characterized. The amino acid sequence is highly homologous to other teleost FELs, containing five repeats of the conserved TECPR domain. Expression of OppFEL was widely observed in examined tissues, with the most abundant transcripts observed in gill, showing a pattern of tissue specific expression. The OppFEL expression was significantly up-regulated following a Gram-negative bacterium (Vibrio anguillarum) challenge in vivo, suggesting participation in host antibacterial immune responses. Recombinant OppFEL protein (rOppFEL) possessed calcium dependent binding capacities and agglutination to four Gram-negative bacterium and two Gram-positive bacterium. Sugar binding assay revealed that rOppFEL specifically bound to insoluble lipopolysaccharide and peptidoglycan. In addition, rOppFEL was also proved to have hemagglutinating activity against erythrocytes from Mus musculus, O. punctatus, Sebastes schlegelii and Paralichthys olivaceus. Dual-luciferase analysis showed that overexpression of OppFEL could suppress the activity of NF-κB in a dose dependent manner. Taken together, these results suggest that OppFEL is a unique fish-egg lectin that possesses apparent immunomodulating property and is involved in host defense against pathogens invasion.

Identification and functional characterization of fish-egg lectin in zebrafish

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.