The arrival of the coronavirus in our lives has made the word immunity part of everyday vocabulary. Antibodies generated after suffering from covid or antibodies provided by vaccines are our allies against SARS-CoV-2. But T cells or lymphocytes also play a fundamental role against this virus.
T lymphocytes. Image courtesy of Melio.
Our immune system, which includes T cells, is made up of a complex network of cells, tissues, and organs that work in concert to recognize and attack foreigners, especially viruses, bacteria, parasites, and fungi that cause disease.
Biologist Teresa Bermejo, from the medical team at Melio (online blood testing platform), explains the types of immunity:
- Innate immunity: It is the first line of defense against a pathogen that generates infection with a rapid reaction but recognizes certain molecules of that foreign microorganism, not all of them, so its specificity is limited.
- Adaptive Immunity: On the other hand, this type of immunity produces a slower but more specific reaction, so its response develops throughout life and protects us against future reinfections. T lymphocytes are part of this immunity.
T lymphocytes in six keys
1. T lymphocytes, a type of adaptive immunity
Inside of adaptive immunity There are, in turn, two types of responses: humoral immunity and cellular immunity. Both responses do not act independently, but their activation and action is coordinated.
- The humoral immunity is mediated by B lymphocytes that produce antibodies or immunoglobulins. These antibodies recognize pathogens, bind to them and neutralize them.
- Cellular immunity: the T lymphocytes They are part of this immune response and are the main defense mechanism against intracellular microorganisms, pathogens that grow and multiply inside the cells of the host they are infecting, such as SARS-CoV2.
The immune response of T lymphocytes is based on detecting and destroying those cells that have been infected. In this way they prevent the microorganism from replicating and spreading the infection. In addition, they release different cytokines and messengers that activate other cells that participate in the immune response.
2. The work of T lymphocytes
T cells are made in the bone marrow. Then they travel to the thymus, a gland where they are going to be “educated” so that they express receptors capable of detecting pathogens and differentiating them from our own cells so that the immune system does not attack the healthy cells of our body.
The newly formed T lymphocytes leave the thymus and circulate through the blood, lymph and secondary lymphoid organs (spleen, lymph nodes, mucous membranes…) and during their journey they can come into contact with a pathogen capable of binding to their receptors and thus become infected. will activate the immune response.
3. What happens when you get infected with COVID-19?
We can get covid when SARS-Cov-2 infects the superficial cells of our airways. T cells will be responsible for identifying and eliminating those cells that have been infected, without damaging those that are healthy and are in the vicinity.
Much of the memory of the immune system is due to these cells. We know that the memory of T cells can last for decades, but we still do not know for how long they provide us with protection against SARS-CoV-2, since it is a too recent virus and not enough time has passed yet to specify it.
4. Do vaccines generate cellular immunity?
The main objective of vaccines is to activate the immune system and achieve a response as similar as possible to that which would be produced by infection by the virus. In this way it is possible to generate memory against a pathogen without the harmful effects of suffering from the disease.
The response of T cells when the COVID-19 vaccine is administered is similar to the response to real infection, which induces these cells to reproduce and generate memory T cells, which will protect us against future infections.
5. Study cellular immunity
If a T lymphocyte that has specific receptors against a pathogen comes into contact with it, it will bind to the proteins on its membrane. This causes that T cell to activate and release a series of molecules called cytokines that will stimulate and regulate the action of other components of the immune system.
The tests that study cellular immunity are based on this process. A sample of the patient’s blood, containing T cells, is brought into contact with fragments of the virus capable of stimulating them. The cytokines released during this process will be detected by different analytical techniques.
6. Cellular immunity and antibody test
Our body is not capable of developing a robust immune response mediated solely by humoral immunity or cellular immunity. For the system to work and offer us an appropriate response, it is necessary for the components of both types of immunity to interact with each other.
This means that, while the T cell-mediated response is important in fighting the coronavirus, it is only half of the immune response, with antibody production (produced by B lymphocytes) being the remaining half.
Carrying out a covid cellular immunity test can tell if an immune response mediated by T cells has been generated after being infected by the SARS-CoV-2 virus or having been vaccinated. However, for a more complete view of the immune response against the virus, it may be advisable to also carry out an antibody or serological test.
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