2021-08-27 18:36:25
The response of our defense system against a microbial invasion follows a pattern that Jorge Laborda has been reeling off throughout the previous chapters dedicated to the Immune System. We have talked about the external barriers that protect us, the skin and the mucous membranes; of first combat forces that intervene when these barriers are overcome, made up of cells and a wide spectrum of molecules that create a true chemical warfare against the invaders. As the invasion progresses, the immune system deploys alarm signals, communications systems, and cells that capture the enemy and present their remains to develop specific weapons against them. Thus we arrive at what is known as adaptive immunity, because it adapts to the specific enemy and develops specific weapons against it. In the previous chapter we talked about B lymphocytes and their weapons, antibodies, a word with which we are familiar due to the pandemic generated by the coronavirus SARS-CoV-2. Many of us have undergone an “antibody test” to find out if we have defenses against the virus. What does this test show and how does it work? The answer requires the introduction of another protagonist. The T lymphocyte
One way to know if a person has generated defenses against the coronavirus is to do an antibody test. These tests do not show the presence of molecules related to the virus, which we call antigens, but rather those that our immune system has generated in response to an infection and which are known as antibodies.
Those who have gone through a test of this type will have verified that the test shows three possibilities (see image): IgM, IgG and C. When we place a drop of blood on the square marked with the letter S and at point B a reactant, a solution is produced by capillarity that runs through the rectangular window with the three marks.
Jorge Laborda explains that both IgM and IgG are antibodies produced by B lymphocytes when the presence of the coronavirus is detected, however, both are generated at different times of the infection. IgM antibodies are generated first and have a dozen binding sites that adhere weakly to coronavirus antigens. When the infection progresses, the generation of improved antibodies is necessary, capable of binding antigens more strongly and thus improving their effectiveness. This is the case of IgG, although to be generated by B lymphocytes the participation of the other protagonist is necessary: the T lymphocyte.
In previous chapters, Jorge Laborda explained that in the first moments of an infection, dendritic cells and macrophages capture bacteria or viruses, engulf and partially digest them. Partial digestion destroys the invader, but preserves some of its characteristics so that they can be safely displayed. Fragments of the enemy generated during digestion are directed to the cell membrane and displayed on the outer surface in order to inform other cells of the immune system of their presence. However, the capture and digestion of the attacking microorganisms is not enough, it is necessary that other cells of the immune system detect the enemy molecules expressed on the surface of the cell and, for this, the dendritic cells must travel to the place where they are located. where these cells are found: the lymph nodes. There the B and T lymphocytes wait.
B lymphocytes detect antigens directly, they do not need other cells as intermediaries to detect them. T lymphocytes, on the other hand, do require the intermediation of other cells to detect antigens. There are many millions of T lymphocytes and they differ from each other due to their ability to detect and bind to specific molecules. Only when a dendritic cell, which has modified its outer covering to display molecules of the invader that it has partially digested, encounters the right T cell to detect those molecules, will the two cells connect, exchange information about the enemy, and trigger T cell activation. .
Although everything is very complex, and T lymphocytes can evolve in different ways depending on the information received, when a T lymphocyte previously “activated” by the encounter with a dendritic cell meets a B lymphocyte that has also engulfed the enemy and presents in its membrane the same molecule that produced its activation, a process begins that enables the B lymphocyte to make a change in the production of antibodies. Thus, the B lymphocyte, thanks to the information received from the T lymphocyte, begins to generate another type of antibody that is more effective in the fight against the invader, it changes from generating IgM to IgG.
Thus, for a time, two populations of B lymphocytes coexist. Initially, the one that generates IgM antibodies is the majority, but as encounters with T lymphocytes occur, the population that generates IgG increases in proportion until it becomes majority. Although the whole process is very complex, it is worth this summary to show why an antibody test fundamentally detects IgM in people who have been recently infected and, as time goes by, the amount of IgM gradually decreases and the IgG antibody that gain prominence. Thus, a person who has generally been infected for a long time will show a single IgG line, as is the case shown in the image.
Of course, Jorge Laborda tells many more things during the interview, I invite you to listen to it.
CHAPTERS ISSUED
We are surrounded! immune system 1.
The chemical warfare of the Immune System 2.
Alarm, we are attacked! Immune system 3
Adapting to the enemy within. immune system 4.
Reporting on the enemy. immune system 5.
B lymphocytes and antibodies. immune system 6
Antibody test and T lymphocytes. Immune System 7
BOOKS:
Your defenses against coronavirus. A brief introduction to the immune system
Your defenses against coronavirus. A brief introduction to the immune system.
Your defenses against coronavirus. A brief introduction to the immune system.
Deflamed immunology: An introduction to the immune system and its pathologies
Deflamed immunology: An introduction to the immune system and its pathologies
Deflamed immunology: An introduction to the immune system and its pathologies
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