Patent Application
20130017536
This kit could differentiate infected poultry from vaccinated during influenza outbreak.
Differentiating infected from vaccinated animals is known as DIVA strategy. Vaccination is primarily performed using killed whole virus-adjuvanted vaccines. Proper vaccination may reduce or prevent clinical signs, reduce virus shedding in infected birds, and increase the resistance to infection.
One limitation of killed whole-virus vaccines is that vaccinated birds cannot be distinguished serologically from naturally infected birds using commonly available diagnostic tests. Thus detection of avian influenza becomes much more difficult and often results in trade restrictions because of the inability in DIVA strategy to distinguish between vaccinated and infected individuals.
The most common method to distinguish vaccinated individuals from infected is the use of unvaccinated sentinels. A second approach is the use of subunit vaccines targeted to the hemagglutinin protein allowing serologic surveillance to the internal proteins. A third strategy is to vaccinate with a homologous hemagglutinin to the circulating field strain, but a heterologous neuraminidase subtype. Serologic detection can then be performed for the homologous NA subtype as evidence of natural infection. A fourth strategy is to measure the serologic response to the nonstructural protein 1 (NS1). The NS1 protein is produced in large quantities in infected cells, but it is not packaged in the virion. Since killed vaccines for influenza are primarily made with whole virions, a differential antibody response can be seen between naturally infected and vaccinated animals. However, poultry vaccines are not highly purified, and they contain small amounts of the NS1 protein.
Although vaccinated chickens will produce low levels of antibody to the NS1 protein, virus infected chickens will produce higher levels of NS1 antibody, and the two groups can be differentiated. All four DIVA strategies have advantages and disadvantages, and further testing is needed to identify the best strategy to make vaccination a more viable option for avian influenza.
In 2005, Terrence M. Tumpey produced recombinant NS1 protein in Escherichia Coli and develops an ELISA and western blot method to measure the antibody in infected poultry against NS1 protein. In this research they show the reaction band in western blot either. Tumpey even introduced two sequences of antigenic peptides in NS1 protein which has an important role in producing antibody.
They developed an ELISA system with these peptides to differentiate the infected and vaccinated poultry, but because of the small size of the peptides, it was not possible to develop a western blot method. ELISA is a colorimetric test and it must be confirmed with the other test like western blot.
In 2007, Laurence Duchesne developed a western blot method for detection of low molecular weight peptides. They made a coated metal like membrane to keep the peptides on the membrane so the peptides will not be washed out through the membrane during washing.
In our project, we applied the conserved peptide of the NS1 protein to detect antibody against peptide antigen in infected poultry to differentiate infected poultry from vaccinated one. This peptide will be transferred from the gel to the silver nanoparticle coated membrane. This will be done through western blot process and the peptide antigen will react with the antibody which is present in infected serum. In fact, this methodology may be generalized to any protein having one or more conserved peptide regions and may thus be used in other contexts wherein it is necessary to differentiate between vaccinated, naturally resistant and infected individuals.
Avian influenza is a viral disease of poultry which causes a wide range of disease symptoms. During avian influenza outbreak, it is difficult to differentiate infected poultry from vaccinated, because the titer of the antibody in vaccinated poultry is high enough to cross linked with the infected poultry serum antibody. It is to be clearly understood that the kit may be used in any context wherein it is desirable to differentiate between vaccinated and infected individuals of any kind such as e.g. humans, cattle, poultry and pork. Consequently, in the context of any infectious disease the kit may be used to discriminate between infected and vaccinated individuals such as e.g. avian influenza or diseases caused by coxsackievirus, hepatitis A virus, poliovirus, rhinovirus, herpes simplex type 1, herpes simplex, type 2, varicella-zoster virus, Epstein-Barr virus, human cytomegalovirus, human herpesvirus, hepatitis B virus, hepatitis C virus, yellow fever virus, dengue virus, West Nile virus, HIV, measles virus, mumps virus, parainfluenza virus, respiratory syncytial virus, human metapneumovirus, papillomavirus, rabies virus, Rubella virus, human bocavirus, parvovirus B19. The kit may thus utilize any conserved part of a peptide or protein of any of the mentioned viruses and the kit may further more use one or more such conserved regions, such as e.g. two or more, such as e.g. 3 or more, such as e.g. 4 or more, such as e.g. 5 or more conserved regions of a peptide or protein of a virus. In this kit two conserved peptide of the NS1 protein is chosen to differentiate infected poultry from vaccinated one. NS1 is a conserved nonstructural protein of influenza A virus. There is very low concentration of antibody against this antigen in vaccinated poultry.
Western blot is an accurate method of assaying a protein in the biologic sample. In general methods of Western blot, samples are applied to a polyacrylamide gel to separate the protein through an electrophoresis technique. The proteins which have been separated into discrete bands, subsequently are transferred to a membrane (Polyvinylidene Fluoride (PVDF) or nitrocellulose), then the membranes are exposed to the antibody. If the antigen is present in the membrane the antibody will bind to it and the excess antibodies which are free in the membrane will washed out. In the next step the membranes are treated with the secondary antibodies which are labeled with a HRP enzyme. The enzyme will react with a substrate and generate colored product. In the case which the substrate is luminol the reaction will be visualized by Chemidoc apparatus, this kind of substrate are more sensitive. This technique is a confirmation test. However, it is to be clearly understood that any substrate that is suitable for detection of fluorescence may be used.
In the western blot of the present study, the antigens are peptides but may also be proteins. Two sequences of the peptides as following are synthesized, Peptide A: NH2-GDAPFLDRLRRDQK—COOH (MW: 1686, 9), and Peptide B: NH2-LRRDQKALKGRGS—COOH (MW: 1484, 73). These peptides are loaded in a Tricine-SDS-PAGE (sodium dodecyl sulfate polyacrylamide gel electrophoresis). The low molecular weight of the peptide during transferring from the gel to the membrane may cause its diffusion through the membrane by applying the voltage. Doing western blot with low molecular weight antigens like peptides is difficult. To keep the peptides in the membrane, silver nanoparticle may be used as blocker against diffusion of the peptides. The high affinity binding of noble metals to proteins is attributed to the affinity of the thiols (SH in Cys) and of the amino groups (Arg,Lys,His,amides of Asn,Gln, and the peptide bond) toward these metals. Consequently, not only silver but e.g. copper, platinum and gold may be used according to the invention applicable to any peptide sequence. The peptides were loaded in the Tricine-SDS-PAGE gel; this gel is commonly used to separate proteins in the mass range 1-100 kDa. It is the preferred electrophoretic system for the resolution of proteins smaller than 30 kDa. The concentration of acrylamide used in this gel is lower than in other electrophoretic systems. These lower concentrations facilitate electro blotting, which is particularly crucial for hydrophobic proteins (Nature Protocol, Hermann Schagger, 2006).
The PVDF membranes which are used in this study could be functionalized with silver nanoparticle.
Colloidal silver nanoparticle (around 10 nm) are used to treat the PVDF membrane, as it avoids peptide diffusion during applying the voltage. The functional group of the amino acids will react to the silver nanoparticle in the membrane. The membrane will be blocked in % 5 BSA. Then the membrane treated with serum and the peptides bind to the antibodies in the infected serum. The membrane is washed to remove unbounded antibody and then treated with the secondary antibody conjugated with HRP enzyme. The membrane is washed to remove unbound conjugated antibody and then it treated with the luminal substrate. Substrate reacts with the enzyme and a colored product will produce from colorless one. The luminal substrate reaction could be visible with a Chemidoc apparatus.
Antibody against NS1 peptide is present in the infected serum and a very low concentration in the serum of the vaccinated poultry. This test could differentiate infected poultry from vaccinated.
The detailed components of the detection kit of this example are listed as follows:
To develop the western blot kit, four kinds of poultry serum provided, first was influenza infected serum collected from infected chickens in the field, second was vaccinated serum collected from chickens which are given influenza vaccine, third was experimental infected serum collected from chickens which are infected with H9N2 antigen and the fourth was normal serum collected from healthy chickens.
Peptide sequence synthesized by Metabion Co. (Germany), antigens (peptides) with 150 ng/μl concentration diluted in sample buffer and run in to the Tricine-SDS-PAGE gel with a size marker, A protein size marker purchased from sigma, Cat NO: M3546 Ultra low range molecular weight marker (M.W. 1060-26600). 16.6% Urea Tricine-SDS-PAGE made by the protocol which is published by Hermann Schagger in Nature Protocols 1, 16-22(2006). Electrophoresis was conducted at 40 v at room temperature and after each 30 min increase the voltage 10 v till 80 v, until the dye front was near the bottom of the gel.
To prepare the Tricine SDS PAGE gel in example 2, the following procedure must be done:
16%/6M Urea Mini Gel:
To do blotting, some parts of the gel which contains peptides must be cut thoroughly from the wells where the peptides loaded. We used PVDF membranes for western blot (sigma: P4188, 0.45 μ). The membranes cut just for the size of the gels. The gels incubated in transfer buffer shaking for 2-5 min. PVDF Membranes must be prepared as following: 1.PVDF must be washed with 70% ethanol, 2. Rinse with water, 3. Incubated 40 min in silver nanoparticle with agitation, 4. Rinse with water twice, 5. Shake the membranes in transfer buffer for 10 min. transfer buffer consists of: Tris 40 mM, Tricine 40 mM, 0.04% SDS, 20% Methanol.
Silver nanoparticle which is used in example 4 was synthesized as following: the products which are needed are: AgNO3, Trisodium citrate, NaBH4. Before Use these buffer must be prepared: 1. silver nitrate at 100 mM (10 ml), 2. Trisodium citrate at 50 mM (10 ml), 3. NaBH4 at 100 mm (10 ml) then 10 mM solution in H2O, all is done in milliQ H2O. Silver nanoparticle synthesizing must be done as the following procedure: 200 ml of H2O in a flask under stirring. Addition of 500 μl of AgNO3 100 mM (0.25 mM final), Wait 1 min then add 1 ml of Trisodium citrate 50 mM (0.25 mM final), Wait 1-2 min and then add 6 ml of NaBH4 10 Mm, solution is getting yellow/brownish very quickly. Around 15 second after the addition of NaBH4 10 mM, the solution is removed from the stirrer, left around 10 min on the bench and then put back on the stirrer for around 30 min.
Transfer the peptides in the gel through the membrane with semidry (Bio-Rad), 30 min 12V. Then the membranes blocked in PBST with 0.5% BSA for 40 min, after incubation they washed with PBS 2 times, then the membranes incubated overnight in infected serum in 4° C. Then the membranes washed 3 times with PBST and then the secondary antibody conjugated with HRP added and incubated for 1.5 hr. The last step is the addition of luminal substrate, which is purchased from sigma with the Cat No.: CPS160-1 Kit and the reaction were seen with Chemidoc (Bio-Rad).
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP10/65626 | 10/18/2010 | WO | 00 | 9/24/2012 |
