COVID-19 has charged straight towards the world, resulting in a pandemic that has left us in a scramble to create an effective vaccine. There is work and research going on around the clock to find an effective treatment and to get an effective vaccine that can then be mass-produced to provide to those who need it most. In the mean time, there is a focus on testing to see if an individual has COVID-19 or not, or has had COVID-19. The accuracy is very important in order to stop the spread of COVID-19. If an individual is asymptomatic and receives a test that says they don’t have COVID-19, they can easily spread it to others around them causing further transmission and more chaos. With accurate testing, once an individual knows they have COVID-19, they can quarantine for 14 days and avoid transmission to others. One of the current methods used for detection is the identification of sufficient amount of viral nucleic acids. However, this method can lead to false negative results. Thus, there are also studies being done to determine if it is more accurate to determine the accuracy of testing the timing and presence of antibodies produced against COVID-19, including IgM, IgA and IgG.
What does the presence of certain antibodies mean?
The evaluation of the timing and amount of different antibodies that act against COVID-19 can allow for the evaluation of how long ago an individual was infected with COVID-19 or if they were even infected at all. If someone is tested and it is found that they only have IgM antibody titers, this is an indication that you have been infected with COVID-19, very recently, they were likely been infected for one to five days. This is because, when infected you make IgM first before any class-switched antibodies are produced, IgM can be produced without receiving further activation from Helper-T cells. If they have both IgM and IgG antibody titers, this is an indication that the individual has been infected with COVID-19 for at least five days. This person’s immune system has undergone class-switching, there are now memory cells being produced and more matured antibodies that have a high affinity for the COVID-19 epitope are released, IgG, which is able to get to all over your body.
Why should we care about this?
Another result that could be important to test for is if the patient primarily has an IgG antibody titer. This likely means that they have been infected for more than five days or that this is their second exposure. This is because, following the fifth day of exposure the IgM response wanes and all cells are class switched to IgG. It could also be their second exposure, because, your memory B-cells expressing IgG (which has a higher affinity) get cross-linked and immediately start secreting IgG, rather than only secreting IgM for five days before you can class switch to IgG. Additionally, if a patient is IgG positive, they won’t be able to infect others. If we could determine who was IgG positive we could determine who has COVID-19 and can potentially determine if COVID-19 has undergone a significant amount of antigenic variation/mutated enough to the point where our COVID-19 antibodies can no longer bind to the same viral spike. Then, we wouldn’t see an IgG positive result, because you would essentially have to start all over again with releasing IgM for five days before you can class switch to IgG. This test is important in being able to efficiently determine who has been exposed and has immunity, and who hasn’t been exposed, and has no immunity, meaning they should be even more cautious.
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