Why do we see zero immunity when we examine birds at 24 days of age to measure the level of immunity to the killed oil vaccine using the ELISA device?
Dr. Milad Ibrahim Arabi
1/8/2024
The type of antigen in the ELISA kit must be known, and the antigen used when examining using the agglutination inhibition (HI) technique must be known.
The titer test must be done using the (HI) method using an antigen isolated from the same company as the killed oil vaccines injected into the bird, for many reasons that I will explain in detail:.
We must understand the antigen present in the ELISA kit and whether this antigen is able to interact with the antibody present in the serum formed as a result of injecting the killed oil vaccine into the chicks.
The agglutination inhibition (HI) test is used to calibrate the antibody response to viral infection. The HI test takes advantage of the ability of some viruses to clump (bind) red blood cells, thus forming a “network” and preventing red blood cells from clumping.
The difference between the two tests:
When testing using the HI technique, there is a complete live virus and this is a natural biological characteristic of the virus in order for Hemagglutination to occur, as the virus binds to blood cells if there are no antibodies associated with it and thus it will form a network of red blood cells, so any mutation in this process will exclude the effect of the virus. A live and strong virus must be used that has the ability to infect, but using vaccines as genes in the HI test is wrong due to the weakness of the virus present in the vaccines. Therefore, I recommend using antigens from the same companies that manufacture killed vaccines.
As for ELISA tests, we must first know what the kit is made of, as most of the kits in ELISA tests are made from fragmented serum types called (monoclonal) and I explained in detail in a previous lecture how they are prepared called monoclonal antibodies. They are the opposite of polyclonal antibodies. That is, the kit contains one epitope that is known and exposed to the antibodies in the serum of the chicken taken for examination, for example, this epitope takes the pathogenic trait ND such as F protein, I will give an example, so this epitope will bind to the antibodies present in the serum, but on the condition that the bird is vaccinated with the same serum type whose titer is to be measured. Therefore, the examination using the ELISA device is very accurate and the detection is more accurate such that any change in the F protein will not be able to be detected, i.e. it gives a negative result.
Meaning that the ELISA test only takes one epitope that is specific or exposed to a virus, enzyme, hormone or pathogen, but on condition that there is a match between the vaccinated serological strain and the epitope present in the kit during the test. For example, when giving a killed vaccine at a certain age, the vaccine contains a virus with more than 1000 epitopes, and when testing, for example, at the age of 25 days using ELISA, the test will search for one exposed epitope known to the company that manufactures the kit, such as the epitope we are looking for is number 3 and the epitope present in the KiT is number 4, and thus no reaction will occur, so a negative result will be skipped in the test, knowing that the bird is vaccinated with the same serological strain.
Therefore, it is not possible to know the epitope present in the KIT because it is a secret of the manufacturing companies. Another important point is that when giving the serum to more than one laboratory, you will notice that there are differences in the test as I explained above, such as the loss of epitope detection. Also, even if you test the serum now and test it after hours, you will notice that there is a difference in the titer, but the problem here is different due to the delay because the virus protein will deform and the ELISA device will not be able to detect it and give a negative result. Or, on the contrary, during the delay, the serum protein may change from a zigzag and coiled thread to a straight thread, and thus all the large peptide bonds will open, and all the epitopes will appear in front of the monoclonal antibodies, and thus the ELISA device will give false high readings. Or damage will occur to the virus protein as a result of the delay and heat, and thus the real epitope will be destroyed and the test will not give any reading. I know that the lecture is complicated and needs explanation and videos. God willing, there will be a practical and theoretical course in two weeks or more. I will explain it in detail and learn about HA and HI tests using real antigen and how to read and diagnose.
Recommendations.
1- Use HI tests (live antigen). In the case of testing antibodies for killed oil vaccines.
2- Use Elisa tests in the case of testing antibodies for live vaccines.
