evolution of immunity after infection

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How does the immune system react when it has to fight the coronavirus? Two scientists scoured the literature to establish a diagram that summarizes the dynamics of adaptive immunity effectors.

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The question ofimmunity generated by the coronavirus SARS-CoV-2 still challenges scientists. Two doctors, one from Emory University in Atlanta, the other from Fred Hutchinson Cancer Research Center of Seattle, have delved into recent scientific literature to try to bring out a general pattern ofimmunity adaptive triggered by the SARS-CoV-2 and its evolution over the weeks. Their point of view was shared by Jama.

Lymphocytes in battle order against the coronavirus

The symptoms from Covid-19 appear between 7 and 10 days after actual infection with SARS-CoV-2. But the immune system is already organizing the counterattack. Lymphocytes T, specific for SARS-CoV-2, begin to proliferate from the first days of infection. The lymphocytes CD4 + T, which act like warlords and polarize the immune response, peak about a week after the first symptoms; CD8 + T lymphocytes, which by their action cytotoxic destroy infected cells, are most numerous between the first and second week of symptoms.

The plasmocytes, the cells that produce the antibody, intervene later. And for good reason, the body’s B lymphocytes are still naive, they have never encountered the antigens of SARS-CoV-2. Once the presentations have been made, the lymphocytes enter into clonal expansion and will undergo several stages until they become mature: first in plasmoblasts, which proliferate as soon as symptoms appear, then in plasma cells producing anti-SARS-CoV antibodies. -2.

Among the pool of B lymphocytes having encountered the antigen, some do not turn into plasma cells, but into memory B cells. If the same pathogenic enters the body again, these memory cells will immediately differentiate into plasma cells. These reserve soldiers are most numerous about two and a half weeks after the onset of symptoms.

The assault on specific antibodies to SARS-CoV-2

Anti-SARS-CoV-2 antibodies peak four weeks after the onset of symptoms. It is then essentially IgM, IgA and IgG. The production of IgG will increase further while the IgM and A will gradually disappear. Seven weeks after the onset of symptoms, plasma cells almost only produce IgG to defend against the coronavirus.

Therefore, the IgG will gradually disappear to reach a low basal concentration about five months after the onset of symptoms. This army, set up against SARS-CoV-2, then entered sleep and will only wake up if a second infection with the same pathogen occurs.

This general diagram describes the evolution of immunity for patients who have developed moderate forms of Covid-19, and who have now recovered. It does not take into account deregulation of the immune system that can be associated with severe forms, nor the immune response of asymptomatic people. In addition, only adaptive immunity is taken into account in this scheme.

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