2023-09-21 08:50:13
September 21, 2023
According to a recent study published in the journal Frontiers in Immunology, two main types of immune responses are involved in the occurrence of long Covid. One is characterized by a very weak immune response, the other by a strong response, causing inflammation. Explanations.
What are the biological mechanisms behind long Covid? This is what researchers from the Institut Pasteur, CNRS and Inserm, in collaboration with the AP-HP, wanted to know. They looked for the production of antibodies and the presence of antiviral T lymphocytes in patients with long Covid. These patients were recruited in 2021 and 2022 within the Persicor cohort, set up at the Hôtel Dieu in Paris.
Two major causes of long Covid have thus emerged: “ nearly a third of patients have a very weak immune response, while the others show a response at least as strong as people who have fully recovered from Covid-19 », notes the Pasteur Institute in a press release dated August 23.
Thus the first group of patients presents persistent viral replication which prevents them from curing Covid. As for the second group, they trigger an immune response that is too strong, or persistent, which creates inflammation, causing long Covid. “Our results suggest that there are several types of long Covid, characterized either by an insufficient antiviral response or by an excessive antiviral response », Specifies Lisa Chakrabarti, researcher in the virus and immunity unit at the Institut Pasteur. In the first case, the tests turn out to be negative, but they are positive in the second.
Ultra-sensitive tests
The researchers succeeded in developing particularly sensitive tests for these “low responder” patients, whose tests remained negative despite the symptoms. Thanks to these tests, scientists managed to observe an immune response, although very weak, in more than half of the patients who were HIV negative during traditional tests. “If validated, these more sensitive laboratory tests might be used to help HIV-negative patients document their infection, and therefore facilitate their access to medical care,” anticipates Lisa Chakrabarti. According to the study, these patients tend to have more symptoms than those with HIV.
This work, the results of which were published in the journal Frontiers in Immunology, tend to prove that there are several types of long Covid. They might make it possible to better care for patients waiting for diagnosis and treatment for sometimes several months.
In France, at the end of 2022, nearly 2 million people had a post-covid condition – long covid – or 4% of the general adult population, according to Public Health France. And around 30% of infected people reported long-term Covid within three months of initial infection. The symptoms of the disease are numerous: muscle and joint pain, severe fatigue, stomach aches, difficulty concentrating, breathing difficulties, etc.
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Source : Divergent adaptive immune responses define two types of long Covid, Frontiers in immunology, July 20, 2023 – Institut Pasteur, August 23, 2023 – Public Health France, June 21, 2023
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Written by : Dorothée Duchemin – Edited by Vincent Roche
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