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Nervous necrosis virus (NNV) has caused severe diseases in global aquaculture industry with tremendous economic and environmental damages. While red-spotted grouper NNV (RGNNV) is the most catastrophic genotype because of plentiful susceptible hosts and expansive distribution ranges. As the only structural protein, capsid protein enables automatic assembly into virus-like particles (VLPs) remaining native infectivity and immunogenicity. In this study, abundant RGNNV VLPs were artificially manufactured and immunized in BALB/c mice, followed by development and characterization of three monoclonal antibodies (mAbs, 2B7, 3A6 and 6E11) subtyped as IgG with a titer of 1:32,000. These mAbs precisely examined two bands (approximately 40 kDa and 120 kDa) of capsid protein by western blot, demonstrating the recognition targets as linear epitopes instead of conformational epitopes. The results of immunofluorescence, immunohistochemistry, immunoprecipitation and immunoelectron microscopy exhibited that all mAbs not only reacted specifically with intracellular viruses, but also exactly labeled free virions, suggesting promising prospects in the detection, localization and tracking of RGNNV. In addition, mAbs 2B7 and 3A6 possessed modest capacity to neutralize RGNNV infection. The pre-incubation of mAbs 2B7 and 3A6 with RGNNV served to suppress the multiplication of virus with 27.99% and 34.37% inhibition ratio, delay the development of cytopathic effect and enhance cell viability by 28.60% and 31.35%, respectively. Taken together, this article proposes several mAbs, which aims at sharing powerful tools for the establishment of potent diagnostics for RGNNV and further investigation into potential pathogenic mechanism. While mAbs 2B7 and 3A6 may advance the intensive development of antibody-based therapeutic countermeasures for RGNNV infection in fish. • VLPs of CNPgg2018 were artificially expressed, assembled and produced in E. coli. • Three mAbs specific for RGNNV were developed successfully. • All mAbs precisely recognized linear epitopes rather than conformational epitopes. • All mAbs specifically reacted with capsid protein and virion of RGNNV. • MAbs 2B7 and 3A6 served to neutralize RGNNV infection and enhance cell viability by 28.60% and 31.35%. [ABSTRACT FROM AUTHOR]

White spot syndrome virus (WSSV) is one of the most serious viral pathogens causing major economic losses to the shrimp farming industry worldwide. Rapid diagnostic test is critical for disease prevention and control. Previously we have developed a rapid immunochromatographic test strip for WSSV detection, but it is limited to the qualitative testing. In this study, a semiquantitative immunochromatographic test strip (SIT-strip) was developed for WSSV detection by observing the number of positive test lines to determine the viral load levels. To achieve semiquantitative analytical ability, three test lines were designed on NC membrane to form the test zone, on which different concentration of anti-WSSV monoclonal antibody (MAb) 4G9 in a decreasing sequence from test line (TL) I to TL-III was dispensed, instead of the traditional application of a single test line. The anti-WSSV MAb 2E6 served as colloidal gold conjugate and goat anti-mouse IgG antibody on control line was used to validate the test performance. The threshold concentrations for TL-I, -II and -III were determined to be 783 ng/ml, 3.13 μg/ml and 6.26 μg/ml of WSSV, respectively, and the visual detection limit of the SIT-strip was 783 ng/ml. The developed SIT-strip was used to detect WSSV at different time points post injection of Procambarus clarkia , the results indicated that one red band was present on TL-I at 12 h post infection (hpi) in the gills, two bands in muscle and three bands in gills and hemolymph were produced at 24 hpi although there was no death at that time, and thereafter three bands were visible in all tested tissues and dead individuals. The mortality was low from 36 to 48 hpi and increased rapidly during 48–72 hpi. Meanwhile, WSSV copy numbers were detected by real time qPCR for severity grading of infection. These results revealed that this SIT-strip could provide confirmation of viral presence and concentration levels prior to mortality, which was early enough to achieve the goal of monitoring for WSSV infection loads predictive of impending disease. [ABSTRACT FROM AUTHOR]

C-type lectins, as types of pattern recognition receptors (PRRs), have crucial roles in innate immunity, and their conserved carbohydrate recognition domain (CRD) is recognized as the binding dominant to pathogen-associated molecular patterns (PAMPs). In this study, a C-type lectin in the scallop Chlamys farreri (lectin B , GenBank No. DQ209290) was heterologously expressed and the recombinant protein (rlectin B) with a molecular mass of approximately 42 kDa was purified. The rlectin B protein could induce the aggregation of Escherichia coli , Vibrio anguillarum and Staphylococcus aureus. Six monoclonal antibodies (mAbs) against rlectin B was developed, among which two mAbs (1A7 and 2B6) could react with the gills, hepatopancreas, adductor muscle, and haemocytes of C. farreri by indirect immunofluorescence assay and bound to proteins with molecular masses of 21, 28, 37, 45, 58, and 70 kDa in western blot assays. Using the two mAbs, C-type lectins protein levels were detected in C. farreri haemocytes after V. anguillarum infection, showing that that lectin levels rapidly increased, peaking at 12 h before gradually decreasing to the control group levels. Furthermore, the FACS results also confirmed that V. anguillarum infection significantly increasing C-type lectins expression in haemocytes. These data suggest that the mAbs can recognize various C-type lectins in C. farreri and are a useful immunological tool for the detection C-type lectins in scallops. • Recombinant C-type lectin (rlectin B) can induce the aggregation of E. coli, V. anguillarum and S. aureus. • Six monoclonal antibodies (mAbs) against rlectin B were developed. • Two specific mAbs reacted with all tissues, especially the haemocytes, gills, hepatopancreas and adductor muscle. • C-type lectin proteins significantly increased in Chlamys farreri haemocytes after V. anguillarum infection. [ABSTRACT FROM AUTHOR]