Jinhua Dong

Open-sandwich immunoassay for sensitive and broad-range detection of a shellfish toxin gonyautoxin.

At present, the analytical method for paralytic shellfish poisoning (PSP) toxins in shellfish is the mouse bioassay (MBA), which is an official method of the Association of Analytical Communities (AOAC [8]). However, the low sensitivity and concerns over the number of live animals required for testing have been cited as the major reason for seeking its replacement. In this report, we employed an open-sandwich immunoassay (OS-IA) to detect gonyautoxin (GTX2/3), a kind of PSP toxins. OS-IA, which utilizes the antigen-induced enhancement of antibody VH/VL interaction, can measure a small molecule antigen in a noncompetitive format. Hence it has a wider working range and shorter measurement time. We isolated anti-GTX2/3 antibody gene from a hybridoma GT-13A by screening a Fab-displaying phage library. Then the vectors for OS-IA were constructed, and examined for antigen concentration-dependency of the VH/VL interaction by OS-ELISA. As a result, in each case, signal intensity increases notably in a wide concentration range (0.1 to >1000 ng mL(-1)) of free GTX2/3, which was enough to cover its regulation value (80 μg 100 g(-1)) in many countries. So OS-IA will be widely applicable to detect PSP toxins in shellfish meats and in drinking water.

Antibody Fab display system that can perform open-sandwich ELISA

Previously, immunological detection of small haptens or peptides was only possible in a competitive format, which needed competitor antigen either labeled by a reporter or attached to a carrier protein. Beside this, open-sandwich immunoassay (OS-IA) is a simple but powerful immunoassay that can noncompetitively determine monovalent antigen concentration by measuring the antigen-dependent increase in V(H)/V(L) interaction of an antibody. However, the procedure to obtain suitable assay reagents for OS-IA for a target antigen has not been straightforward because of the lack of easy-to-use antibody selection/manipulation methods. Here we devise a new Fab antibody phage display system that is useful for rapidly evaluating and selecting suitable antibody Fv fragments to OS-IA. The system is based on a phagemid vector in which two identical restriction sites were incorporated into both ends of a human constant region domain. After selection of the M13 phage displaying a Fab fragment, the vector can be easily converted to the vector that can simultaneously produce the V(H)-displaying phage and the light chain in the culture supernatant, which can be directly used for OS-ELISA. The successful results of model selection as well as conversion to OS format show the potential in developing various OS-IA for clinically and environmentally important targets.

Expression, purification and antigenicity of Neospora caninum-antigens using silkworm larvae targeting for subunit vaccines.

Infection of Neospora caninum causes abortion in cattle, which has a serious worldwide impact on the economic performance of the dairy and beef industries. Now, inexpensive and efficacious vaccines are required to protect cattle from neosporosis in livestock industry. In this study, N. caninum surface antigen 1 (SAG1) and SAG1-related sequence 2 (SRS2) were expressed in hemolymph of silkworm larvae as a soluble form. Expressed SAG1 and SRS2 clearly showed antigenicity against N. caninum-positive sera of cow. SAG1 and SRS2 were purified to near homogeneity from hemolymph of silkworm larvae using anti-FLAG M2 antibody agarose: approximately 1.7 mg of SAG1 from 10 silkworm larvae and 370 μg of SRS2 from 17 silkworm larvae. Mice that were injected by antigens induced antibodies against SAG1 and SRS2. This study indicates that it is possible that this silkworm expression system leads to a large-scale production of N. caninum-antigens with biological function and low production cost. Bombyx mori nucleopolyhedrovirus (BmNPV) bacmid expression system paves the way to produce largely and rapidly these recombinant antigens for its application to subunit vaccines against neosporosis in cattle.

Development of two murine antibodies against Neospora caninum using phage display technology and application on the detection of N. caninum.

Neosporosis, caused by an intracellular parasite, Neospora caninum, is an infectious disease primarily of cattle and dogs. It occurs worldwide and causes huge damages to dairy farms. In this study, we immunized mice with recombinant surface-associated protein 1 of N. caninum (rNcSAG1) and developed two novel monoclonal antibodies, A10 and H3, against NcSAG1 using phage-display technology. Both clones bound to purified rNcSAG1 and the half maximal inhibitory concentrations of A10 and H3 are 50 and 72 nM of rNcSAG1, respectively. In immunofluorescence assays, both A10 and H3 Fabs bound to N. caninum parasites. Direct detection of N. caninum parasites was developed firstly using an enzyme-linked immunosorbent assay (ELISA) with A10 and H3. Binding of A10 and H3 antibodies to rNcSAG1 was also inhibited by some certain anti-N. caninum antibodies in the neosporosis-positive cattle sera, suggesting they might bind to the same epitopes of NcSAG1 with those anti-N. caninum antibodies of bovine. These antibodies were demonstrated to have a potential for monitoring the N. caninum parasites in a dairy farm, which may lead to protect livestock from parasite-infection.

Detection of small molecule diagnostic markers with phage-based open-sandwich immuno-PCR.

Open sandwich immunoassay (OS-IA) utilizes antigen-dependent stabilization of antibody variable region to quantify various antigens, enabling noncompetitive detection of small molecules with a broad working range. To further improve its detection sensitivity, here we employed phage-based immuno-PCR approach, wherein OS-IA and quantitative PCR methodologies were combined with the use of immobilized V(L) fusion protein and filamentous phages displaying V(H) fragment, whose DNA was extracted for PCR amplification. This approach significantly enhanced the assay sensitivity for small molecule antigens osteocalcin (BGP) peptide and 17beta-estradiol.

Display of Neospora caninum surface protein related sequence 2 on Rous sarcoma virus-derived gag protein virus-like particles

Virus-like particles (VLPs) displaying antigen have been increasingly recognized as a potential vaccine in the livestock industry. In this study, Neospora caninum surface protein related sequence (NcSRS)2 was displayed on the surface of Rous sarcoma virus group-antigen protein (RSV-gag) VLPs. Two types of Bombyx mori nucleopolyhedrovirus (BmNPV) bacmids, encoding RSV-gag and NcSRS2 genes, were co-injected into silkworm larvae to produce VLPs-NcSRS2. At 7 days post-injection, VLPs-NcSRS2 were collected from hemolymph and purified. The antigenicity of the purified protein was confirmed by enzyme-linked immunosorbent assay (ELISA) using neosporosis-positive bovine serum. ELISA revealed that ~0.16μg rNcSRS2 was displayed per 1μg VLPs-NcSRS2. To develop an antibody specific for VLPs-NcSRS2, purified VLPs-NcSRS2 were used to immunize mice in a three-dose regimen without adjuvant and the production of antibodies was confirmed in serum samples. By using a silkworm expression system, we demonstrated the display, expression and immunization of neosporosis-targeting membrane proteins, which are vaccine candidates for neosporosis.

Development of a diagnostic method for neosporosis in cattle using recombinant Neospora caninum proteins

BackgroundNeosporosis is an infectious disease primarily of cattle and dogs, caused by intracellular parasite, Neospora caninum. Neosporosis appears to be a major cause of abortion in dairy cattle worldwide and causes to huge economic loss to dairy industry.ResultsRecombinant surface associated antigen 1 (NcSAG1), NcSAG1 related sequence 2 (NcSRS2) and the dense granule antigen 2 (NcGRA2) of N. caninum were expressed either in silkworm or in Escherichia coli and purified. The purified recombinant proteins bound to the N. caninum-specific antibodies in serum samples from infected cattle as revealed by an enzyme-linked immunosorbent assay (ELISA). By co-immobilizing these recombinant proteins, a novel indirect ELISA was developed for detection of neosporosis. With the use of 32 serum samples, comprising 12 positive serum samples and 20 negative serum samples, the sensitivity and specificity of the assay were found to be 91.7 and 100%, respectively. Seventy-two serum samples from dairy farms were also tested and one was diagnosed with neosporasis with both this method and a commercial assay.ConclusionsA diagnostic method employing recombinant proteins of N. caninum was developed. The method showed high sensitivity and specificity. Diagnostic test with field serum samples suggested its applicability to the practical diagnosis of neosporosis.

Isolation of Recombinant Phage Antibodies Targeting the Hemagglutinin Cleavage Site of Highly Pathogenic Avian Influenza Virus

Highly pathogenic avian influenza (HPAI) H5N1 viruses, which have emerged in poultry and other wildlife worldwide, contain a characteristic multi-basic cleavage site (CS) in the hemagglutinin protein (HA). Because this arginine-rich CS is unique among influenza virus subtypes, antibodies against this site have the potential to specifically diagnose pathogenic H5N1. By immunizing mice with the CS peptide and screening a phage display library, we isolated four antibody Fab fragment clones that specifically bind the antigen peptide and several HPAI H5N1 HA proteins in different clades. The soluble Fab fragments expressed in Escherichia coli bound the CS peptide and the H5N1 HA protein with nanomolar affinity. In an immunofluorescence assay, these Fab fragments stained cells infected with HPAI H5N1 but not those infected with a less virulent strain. Lastly, all the Fab clones could detect the CS peptide and H5N1 HA protein by open sandwich ELISA. Thus, these recombinant Fab fragments will be useful novel reagents for the rapid and specific detection of HPAI H5N1 virus.

Expression and purification of bioactive hemagglutinin protein of highly pathogenic avian influenza A (H5N1) in silkworm larvae

The hemagglutinin (HA) of avian influenza viruses plays a very important role in the infection of host cells. In this study, the HA gene of the highly pathogenic avian influenza H5N1 virus was cloned and expressed in silkworm larvae. The expressed recombinant HA (rHA) was purified using fetuin-agarose chromatography and Superdex 200 10/300 GL gel filtration chromatography, and the identity of purified rHA was confirmed by SDS-PAGE and Western blot. Approximately 500 μg of purified rHA was obtained from a total of 30 silkworm larvae, suggesting the high efficiency of the silkworm expression system. The purified rHA bound to a rabbit polyclonal antibody against influenza A virus H5N1 (avian flu) HA, suggesting its antigenicity and potential application in vaccine development. Gel filtration chromatography showed that purified HA was present in the void volume fractions, indicating that rHA may form an oligomer. The rHA bound to poly{Neu5Acα2,3LacNAcβ-O[(CH₂)₅NHCO]₂(CH₂)₅NH-/γ-PGA}, which mimics an avian type receptor, but did not bind to γ-polyglutamic acid or human type receptor mimic, poly{Neu5Acα2,6LacNAcβ-O[(CH₂)₅NHCO]₂(CH₂)₅NH-/γ-PGA}, suggesting that it could be utilized as a blocking agent against infection by highly pathogenic influenza viruses.

Simultaneous Retention of Thermostability and Specific Activity in Chimeric Human Alkaline Phosphatases

Alkaline phosphatases (APs) are a family of dimeric metalloenzymes that has been utilized in many areas due to its ability to hydrolyze a variety of phosphomonoesters. While mammalian APs have higher specific activity than prokaryotic APs, they are generally less thermostable. To cultivate the possibility to confer mammalian APs with higher thermostability as well as high activity, we focused on human AP isozymes. Among the four isozymes of human APs, placental AP (PLAP) retains the highest thermostability, while intestinal AP (IAP) has the highest specific activity. Since the two APs display high homology, a series of chimeric enzymes were made in a secreted form to analyze their properties. Surprisingly, chimeric APs with IAP residues at the N-terminal and PLAP residues at the C-terminal regions showed higher specific activity than PLAP, while keeping thermostability as high as PLAP. Especially, one showed similar specific activity to IAP, while showing slower inactivation than PLAP after incubation at 75xa0°C. Interestingly, the mutant also showed higher resistance to uncompetitive inhibitors Phe and Leu than their parent enzymes, possibly due to increased hydrophilicity of the active site entrance residues. The obtained chimera will be useful as a novel reporter in various assays including gene hybridization.