Due to the recent pandemic, there has been a lot of talk about antibodies and how their presence in the blood can serve as an indicator of protection against coronavirus infection. However, what kind of antibodies are we referring to? Is it always good to have high levels of all your antibodies? And more importantly, are all our antibodies the same?
Many types of antibodies for very different functions
Our immune system has several lines of defense, and antibodies are part of the humoral response. In simple terms, the humoral response is one that is not carried out by immune cells, but by molecules that are distributed throughout the body and are usually detected in the blood. Antibodies are a type of security element, which patrols the blood, detecting if something enters from the outside that could pose a threat and, in that case, sound the alarm.
Antibodies, or immunoglobulins, are classified according to their structure and we have five classes: IgA, IgD, IgE, IgG and IgM. They all have a part that is the same and a variable that is different in each class. The variable part is what determines to a large extent the function it has within the organism, but we cannot classify them into good and bad antibodies, because that will also depend on whether they recognize elements of the organism or those of the outside.
A ”glitch” in our immune system
To better understand the dual function that each antibody can have, let’s take the example of allergies. People who suffer from this disease have specific antibodies (IgE) for food proteins or pollen that are not actually dangerous to our body. It could be said that it is a failure of our body to have defenses that are activated against elements that should not be activated because they are not going to harm us. When this IgE comes into contact with its allergen, it activates a series of cells that will be responsible for causing symptoms: itchy eyes, red skin, sneezing, asthma or even anaphylaxis. The higher the IgE levels in the blood, the greater the risk that the symptoms will be more severe.
On the other hand, a person who does not have allergies will most likely have no specific IgE to almost any allergen and their total blood IgE levels will remain in the low range. In the context of allergies, it is not convenient to have high levels of antibodies in the blood.
However, the situation is the opposite when an allergic person receives a treatment called immunotherapy, based on modifying components of the immune system. During the process, antibody levels will change over time and an essential factor is what happens to the IgG-type antibodies. During the first weeks of immunotherapy, in which the patient is continuously exposed to the allergen in question, the levels of IgE in the blood may increase. Shortly thereafter, this IgE will eventually drop to intermediate levels, although it may never reach the very low levels found in non-allergic people.
The most interesting thing and one of the keys by which the patient achieves tolerance to the allergen and stops presenting symptoms is that the blood levels of another type of antibody, IgG, which are specific for the allergen will increase while lowering IgE. Specifically, it is an antibody known as “blocking” or “neutralizing” IgG. Not all IgG have the same function, but if immunotherapy is successful, these IgG blockers in the blood detect the allergen better than IgE and thus prevent the appearance of symptoms.
And what about antibodies and COVID-19?
In the case of a coronavirus infection or after vaccination, we also use blood IgG levels to determine if an immune response has taken place. Again, we refer to these neutralizing IgGs that are responsible for detecting the threat from abroad, in this case the coronavirus , and send the necessary signals to get rid of the threat without suffering great damage.
The levels of antibodies in the blood can be a very useful indicator to get an idea of the processes that our immune system carries out, but it is a simple frame in the middle of a movie. There are many other variables that are important and antibody subtypes that have very different functions. For all these reasons, not all antibodies are the same and the key lies in having the right levels of each type.
References:
Murphy et al. 2008. Janeway’s immunobiology. New York: Garland Science. 9th edition.
Santos et al. 2015. IgG4 inhibits peanut-induced basophil and mast cell activation in peanut-tolerant children sensitized to peanut major allergens. J Allergy Clin Immunol . doi: 10.1016/j.jaci.2015.01.012.
Kelsen et al. 2022. SARS-CoV-2 BNT162b2 vaccine-induced humoral response and reactogenicity in individuals with prior COVID-19 disease. JCI Insight. doi: 10.1172/jci.insight.155889.
