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To determine furaltadone metabolites 5-methylmorpholino-3-amino-2-oxazolidinone (AMOZ) residual levels in ctenopharyngodon idellus, direct competitive enzyme-linked immunosorbent assay (dcELISA) was developed based on a single-chain variable fragment (scFv)-alkaline phosphatase (AP) fusion protein. Firstly, VH and VL gene sequences were cloned from hybridoma cell lines secreting monoclonal antibody against AMOZ derivative, and then the productive VH and VL genes were assembled to a scFv gene and engineered to produce scFv-AP fusion protein. The fusion protein was further identified as a bifunctional reagent for immunoassay, then a sensitive one-step dcELISA against AMOZ derivative was developed with a half-maximal inhibitory concentration (IC50) and limit of detection (LOD) of 10.62 and 4.83 ng/mL, respectively. The recovery values of AMOZ from spiked fish samples determined by dcELISA were in 71.31%∼82.88%. The results suggested that the prepared scFv-AP fusion protein in this work can be used for rapid and convenient immunoassays to detect AMOZ residues in fish samples.

Ovotransferrin (OVT) is one of the major proteins in avian albumen that exerts diverse biological activities. This study is aimed to investigate the antiviral effect and mechanism of OVT from the avian egg. Effects of OVT on vesicular stomatitis virus (VSV)-infected mouse peritoneal macrophage were detected by real-time quantitative polymerase chain reaction, enzyme-linked immunosorbent assay, and western blot. In OVT-pretreated mouse peritoneal macrophages, results showed that replication of VSV was significantly suppressed and production of type I interferon (IFN) was increased. OVT down-regulated ring finger protein 125 (RNF125) production and up-regulated retinoic-acid-inducible gene I (RIG-I) expression by the nuclear factor-κB signalling pathway, resulting in the enhancement of the production of type I IFN. It demonstrated that the antiviral effect of OVT on innate immunity is enhanced by promoting type I IFN expression, indicating its potential as a functional food ingredient.