are we protected after an infection? Response from two researchers

What do we currently know about immune memory in patients who have recovered from SARS-CoV-2 infection? ABSMARTHEALTH went to ask two experts who work on the immune system.

Are we protected after SARS-CoV-2 infection? The re-emergence of cases already infected in South Korea raises fears of a weak immunity after an infection with SARS-CoV-2. So what do we know about the antibody response generated by our body? Overview of the subject in this ehealth with two experts.

This new virus, Which appeared a few months ago, is full of mystery. If we could quickly decipher her genome, we’re still a long way from knowing what’s going on whenit interacts with our organism. Among all these questions, that of the immune memory torments us. After SARS-CoV-2 infection, are we protected? What happens to our lymphocytes to memory? Are there any? In everyone? If yes how much ? Have they acquired increased longevity? Are they robust? Or are they fragile with a short duration of life ? So many questions that scientists must answer in a fierce race against the progression of pandemic.

Some reminders on the immune system

Our immune system is eminently complex machinery. We can not the booster at the click of a finger. Thanks to advances in biology, technologies and of the scientific method, we know a little more about it. However, we are far from grasping all the ins and outs. To make reading easier, let's tell a story, a bit like in the cartoon Once upon a time the life.

Imagine your organism as a small Greek city. You have soldiers (macrophages, dendritic cells, NK cells, granulocytes) That rotate continuously to ensure that no one is attacking your city. These can trigger what is called the innate immune response. It generally results in inflammatory reactions. In addition to that, you have couriers (cell presentingantigens) who, when the soldiers are overwhelmed, bring the suspect to your generals (B and T lymphocytes). In reality, some of the soldiers described (macrophages, dendritic cells) have the ability to differentiate themselves and transform themselves into couriers when they encounter molecules clean pathogens ((nucleic acids viral or bacterial for example). The lymphocytes-general scan the uniform of the attacker (protein particular) and its decorations (other particular characteristics, generally of a protein nature) when it occurs. It's all part of the adaptive immune response.

Subsequently, they will create weapons ( antibody appointed immunoglobulins) Specialized in the combat of specific attackers (humoral immune response) where they will drop bombs (molecules cytotoxic, as granzyme B, which have the capacity to kill infected cells) on attackers (cellular immune response). In either case, they will normally train other generals in mass. The latter, better trained and better armed, will be ready to react faster and stronger when the pathogen resurfaces. This is called immune memory.

Immune memory therefore designates a population of lymphocytes (B or T) having acquired new or increased functional properties allowing the organism to defend itself with much more efficiency during re-exposure to a pathogenic agent already encountered in the past. This is how it works vaccines. However, whether it be infections or vaccines, theimmunity conferred is variable and sometimes borrows different mechanisms.

As Branka Horvat, director of the Immunobiology of viral infections team at the International Center for Research in Infectious Disease of Lyon, explains to us, “ being infected and not producing a lot of antibodies does not necessarily mean that you are not protected; indeed, it is also necessary to assess the cellular immune response, which is more difficult to measure than the humoral response. " The vaccine against the virus measles for example, immunizes us for life while the protection conferred by the vaccine against tetanus faints over time, therefore requiring vaccine reminders. To maintain immunity, it is the subject of several reminders in a person's life.

Immune memory and SARS-CoV-2

In South Korea, several cases of people having overcome the disease, with no detectable antibody production, have been reported. But in reality, there are several hypotheses to define this phenomenon. As Thierry Defrance, director of the effector and memory B lymphocytes team at the International Center for Infectious Disease Research in Lyon, explains: “There are several hypotheses. Either it is a resurgence of symptoms without the virus being detectable again. In this case, it would be a kind of startle of the immune system at a distance from the primary infection (for example a second thunderstorm cytokine but without triggering viral cause). Or, what seems to me more likely, is a re-expression of the virus which would have hidden in certain protected sites of the body, less accessible to the immune response and which could reactivate when the pressure of the immune system is weaker. This raises the question of a possible defect in the generation of immune memory during the primary infection. But this probably does not represent the majority of cases for which a memory seems effectively generated. The pre-published Chinese study showing that 70% of infected patients make neutralizing antibodies and the fact that plasma from post-infection patients can be transferred to newly infected patients to neutralize the virus thereby evidencing neutralizing antibodies circulating in post-infection patients. "

We can also think of a diagnostic failing during the supposed first infection or other hypotheses, unknown until now, which should not be concealed before further investigation.

The reality is that we don't know much, but we learn quickly. A prepublished study Chinese (the one Thierry Defrance was talking about, above) suggests that there is an antibody response but that it is quite variable. The duration and robustness of this immune memory in those who benefit from it is also unknown. As mentioned the day before yesterday the Minister of Health Olivier Véran, for the moment several hypotheses are under study and we have to wait for science to decide on the facts, because that is its role.

To understand why, we have to remember how science works. Science is not a big book with all the knowledge written in it. Scientists are just the opposite of people who claim to know everything. They learn by dint of theories, experiences and confrontation with reality. As soon as a new phenomenon appears (here, theemergence of a new virus), unfortunately, we are in the unknown. This is what characterizes scientific work. Navigate in uncertainty and confront your hypotheses with reality. Only the confrontation of the hypothesis with the experimental data gives rise to knowledge. Scientist is not a great sage who creates truth ex nihilo.

This must be kept in mind in order to understand why, in this crisis we are going through, we hear so frequently "Let's be careful", "we don't know yet", "scientists are working hard, they must be given the time to produce knowledge". Scientific work is methodical. It requires persistence and thoroughness. For all these reasons, it is exciting, tedious and ungrateful. We have to face reality. And, often, we take it in the face when we find that our hypothesis is false.

On the other hand, the general public expects scientists to know. This shows a poor understanding of what science is by the people. Is it the fault of scientists who do not popularize enough? National education which does not make our schoolchildren sufficiently aware of the history of science? Or to citizens who are too disinterested in these questions? This is not the subject here. What we can all the same say is that without knowing what the sciences are, we are immersed in the relativism of statements.

More deeply, we face the fear of uncertainty. Understanding the sciences better and working on yourself means being able to better accept this uncertainty in the world instead of getting bogged down in false truths that reassure us and prolong the duration of uncertainty. We hope that this crisis will at least have the merit of showing the general population that science is above all about swimming in uncertainty. As for us, citizens, it will allow us, perhaps, to learn to live with the latter which is, in reality, omnipresent in our lives.

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