Establishment and Optimization of Monoclonal Antibody-based Heterologous dcELISA for 19-Nortestosterone Residue in Bovine Edible Tissue

Indirect Competitive ELISA for the Determination of Total Chromium Content in Food, Feed and Environmental Samples

Background: This study aimed to prepare monoclonal antibodies (mAbs) with high immunoreactivity, sensitivity, and specificity for the chelate (Cr(III)-EDTA) of trivalent chromium ion (Cr(III)) and ethylenediamine tetraacetic acid (EDTA). Further, the study established an indirect competitive enzyme-linked immunosorbent assay (icELISA) for detecting the total chromium content in food, feed, and environmental samples. Methods: Hapten Cr(III)-iEDTA was synthesized by chelating Cr(III) with isothiocyanatebenzyl-EDTA (iEDTA). Immunogen Cr(III)-iEDTA-BSA formed by chelating Cr(III)-iEDTA with bovine serum albumin (BSA), and coating antigen Cr(III)-iEDTA-OVA formed by chelating Cr(III)-iEDTA with ovalbumin (OVA) were prepared using the isothiocyanate method and identified by ultraviolet spectra (UV) and inductively coupled plasma optical emission spectrometry (ICP-OES). Balb/c mice were immunized with the Cr(III)-iEDTA-BSA, and the anti Cr(III)-EDTA mAb cell lines were screened by cell fusion. The Cr(III)-EDTA mAbs were prepared by induced ascites in vivo, and their immunological characteristics were assessed. Results: The immunogen Cr(III)-iEDTA-BSA was successfully synthesized, and the molecular binding ratio of Cr(III) to BSA was 15.48:1. Three hybridoma cell lines 2A3, 2A11, and 3D9 were screened, among which 2A3 was the best cell line. The 2A3 secreted antibody was stable after six passages, the affinity constant (Ka) was 2.69 × 109 L/mol, its 50% inhibition concentration (IC50) of Cr(III)-EDTA was 8.64 μg/L, and it had no cross-reactivity (CR%) with other heavy metal ion chelates except for a slight CR with Fe(III)-EDTA (1.12%). An icELISA detection method for Cr(III)-EDTA was established, with a limit of detection (LOD) of 1.0 μg/L and a working range of 1.13 to 66.30 μg/L. The average spiked recovery intra-assay rates were 90% to 109.5%, while the average recovery inter-assay rates were 90.4% to 97.2%. The intra-and inter-assay coefficient of variations (CVs) were 11.5% to 12.6% and 11.1% to 12.7%, respectively. The preliminary application of the icELISA and the comparison with ICP-OES showed that the coincidence rate of the two methods was 100%, and the correlation coefficient was 0.987. Conclusions: The study successfully established an icELISA method that meets the requirements for detecting the Cr(III)-EDTA chelate content in food, feed, and environmental samples, based on Cr(III)-EDTA mAb, and carried out its preliminary practical application.

The Rapid Screening of Triazophos Residues in Agricultural Products by Chemiluminescent Enzyme Immunoassay

A highly sensitive chemiluminescent enzyme immunoassay (CLEIA) method was developed in this study for efficient screening of triazophos residues in a large number of samples. Based on the maximum residue limits (MRLs) set by China and CAC for triazophos in different agro-products, the representative apple, orange, cabbage, zucchini, and rice samples were selected as spiked samples, and the triazophos at the concentrations of the MRL values were spiked to blank samples. Subsequently, the five samples with the spiked triazophos standard were measured by CLEIA 100 times, and the detection results indicated that the correction factors of the apple, orange, cabbage, zucchini, and rice were determined as 0.79, 0.66, 0.85, 0.76, and 0.91, respectively. In this experiment, 1500 real samples were detected by both the CLEIA and the GC-MS methods. With the GC-MS method, 1462 samples were identified as negative samples and 38 samples as positive samples. Based on the correction factors, the false positive rate of the CLEIA method was 0.13%, and false negative rate was 0. The results showed that the established CLEIA method could be used to screen a large number of real samples.

The potato mop-top virus TGB2 protein and viral RNA associate with chloroplasts and viral infection induces inclusions in the plastids

The potato mop-top virus (PMTV) triple gene block 2 (TGB2) movement proteins fused to monomeric red fluorescent protein (mRFP-TGB2) was expressed under the control of the PMTV subgenomic promoter from a PMTV vector. The subcellular localizations and interactions of mRFP-TGB2 were investigated using confocal imaging [confocal laser-scanning microscope, (CLSM)] and biochemical analysis. The results revealed associations with membranes of the endoplasmic reticulum (ER), mobile granules, small round structures (1-2 μm in diameter), and chloroplasts. Expression of mRFP-TGB2 in epidermal cells enabled cell-to-cell movement of a TGB2 defective PMTV reporter clone, indicating that the mRFP-TGB2 fusion protein was functional and required for cell-to-cell movement. Protein-lipid interaction assays revealed an association between TGB2 and lipids present in chloroplasts, consistent with microscopical observations where the plastid envelope was labeled later in infection. To further investigate the association of PMTV infection with chloroplasts, ultrastructural studies of thin sections of PMTV-infected potato and Nicotiana benthamiana leaves by electron microscopy revealed abnormal chloroplasts with cytoplasmic inclusions and terminal projections. Viral coat protein (CP), genomic RNA and fluorescently-labeled TGB2 were detected in plastid preparations isolated from the infected leaves, and viral RNA was localized to chloroplasts in infected tissues. The results reveal a novel association of TGB2 and vRNA with chloroplasts, and suggest viral replication is associated with chloroplast membranes, and that TGB2 plays a novel role in targeting the virus to chloroplasts.