This is part 2 of 4 of our Understanding Antibodies segment. See our previous blog on IgM antibodies if you are just catching up!
Immunologic Memory – The Key to IgG
So last time we talked about the immune system and how it works. How the immune system uses both the innate and adaptive immune system to fight infection. To understand IgG antibodies, we are going to dig a little deeper into how the adaptive immune system works.
The key to IgG antibodies lies in immunologic memory. What on earth does this mean!? Well in short, it is a process in the immune system that creates a memory of things its fought before. The immunologic memory is important. If the immune system can remember what it fought and how it fought it in the past, the next time it encounters it, it can kill that thing faster. This is how vaccines work.
When we give someone a vaccine, we are giving them a little piece of a virus to help create memory. When the immune system detects that piece of a virus the first time, it builds a strategy to fight it. Every time it gets exposed to that virus it will be able to fight it faster and better. This is why some vaccines need boosters or multiple shots – to help the immune system create a stronger and faster response. IgG antibodies are the main contributors to this memory.
Types of Antibodies: IgG
IgG antibodies are the main antibodies found in the immune system. They represent approximately 75% of all antibodies in the blood. These antibodies are found everywhere and are a part of EVERYTHING. If we were to stick with my Umbrella Academy reference, IgG’s would be considered the Number 5 of the family. (You know, the one that gets into things they should and shouldn’t and are everywhere all at once??)
IgG antibodies have incredible binding power. They can bind to a number of different organisms at one time. They are also the antibodies that can neutralize pathogens. And they are the main antibodies that call in the T-cells that known for their incredible destructive power.
Unlike IgM antibodies, IgG antibodies take long time to ramp up and ramp down. After an initial infection, IgG antibodies will take approximately 3-6 weeks to rise. IgG antibodies also have a half life of 21 days (3 weeks), which means that once they are elevated they stick around a lot longer. This is why they helpful for immunologic memory. After a vaccine or infection, if IgG antibodies can stay elevated, they will help someone fight an infection in the future.
Clinical Relevance of IgG
Because IgG’s are the most prevalent of the antibodies, they are some of the most important ones to track. And because they can indicate memory to an infection, they are often used to see if someone is immune to an infection.
For COVID-19, IgG antibodies are the ones that are most tested for. Our hope is that if people mount enough IgG antibodies in response to COVID-19 they will be immune. But our reliance on this is tricky. The antibodies must be high enough and the immune system had to effectively fight the infection when it was present. While IgG antibodies, when elevated, are a good indicator you had an infection sometime in the last few months, we can’t tell for certain if that means that you are immune.
IgG antibodies are incredibly important for autoimmune diseases. For autoimmune diseases where antibodies are present in the blood (Hashimoto’s, Lupus, Rheumatoid Arthritis…etc), they are a good indicator of that disease. They can also be measured over a period (months and years) to see if they go down or up with treatment. Monitoring IgG antibodies can be a good tool to tell if a treatment is or isn’t working with time.
IgG antibodies are easy to measure in the blood stream. If you are interested in getting COVID-19 IgG testing or antibodies tested for certain diseases, talk to your doctor. We also offer many different types of antibody testing in our office as well. In a few weeks, we will go through IgA antibodies.
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