A Franco-Portuguese study recently observed that the long Covid could be induced by abnormalities of the immune system associated with the persistent presence of the virus in the intestinal mucous membranes.
- The long Covid is characterized by persistent symptoms beyond four weeks.
- At present, very few biological criteria make it possible to diagnose long Covid, apart from the persistence of symptoms.
- Researchers conducted a study to better understand this prolonged form of the disease and to identify diagnostic markers.
We speak of long Covid when the symptoms linked to Covid-19 persist beyond four weeks. Patients can then suffer from prolonged signs such as fatigue, respiratory and digestive disorders, eye problems or abnormalities of the senses. In some cases, the improvement of the manifestations is slow, sometimes even incomplete.
How to diagnose long Covid?
In addition to the persistence of symptoms over a long period, very few biological criteria make it possible to diagnose long Covid. Scientists from Inserm and Université Paris Cité in collaboration with the University of Minho in Braga (Portugal) conducted a study to better understand this prolonged form of coronavirus and to identify diagnostic markers. Their work has been published in the journal Kind Communication.
For the purposes of this research, the teams examined the immune systems of 164 people six months after their infection. The scientists then analyzed blood samples from 127 participants, half of whom had persistent symptoms from Covid-19 infection, and 37 people who had not developed the disease.
The study authors also studied blood samples taken during the acute phase of the infection from 72 patients. They were then able to compare the level of inflammation at an early stage in volunteers who had developed a long Covid or not. During the study, the researchers also observed T lymphocytes, in particular CD8 cells, which play a role in the elimination of the virus, and the antibodies directed against SARS-CoV-2.
The presence of blood markers in patients with long Covid
According to their results, blood markers were present in 70 to 80% of people who had been affected by a long Covid six months after infection while these blood markers were rare in the other participants who did not develop a long form of the disease. disease.
“The teams have shown in particular that a CD8 cell subtype expressing granzyme A, an inflammatory protein, is in excess, while another CD8 subtype expressing integrin b7 is in low quantity. The latter subpopulation is essential to control viruses in the mucous membranes. In addition, virus-specific IgA antibodies are also in excess, whereas they should be rapidly eliminated if the virus is absent. These observations suggest the persistence of the virus in the body and in particular in the mucous membranes”can we read in the press release from Inserm.
The researchers also found an association “between an inflammatory response characterized in particular by very high levels of interferon IP-10 or interleukin IL-6 and the risk of having a long Covid afterwards” when they observed the initial level of inflammation during the acute phase of Covid-19.
Covid long: the virus could settle permanently in the intestinal mucous membranes
“This confirms clinical observations according to which the initial severity of Covid is associated with a higher risk of developing a long Covid (…) One of the hypotheses is that people who present a more exacerbated immunodeficiency early on develop more severe initial forms of Covid-19 and fail to effectively eliminate the virus which passes into the intestinal mucous membranes, where it settles in. The immune system somehow ends up tolerating it at the cost of persistence of symptoms of intensity and variable nature”indicated Dr. Jérôme Estaquier, researcher at Inserm, who directed this work.
In the future, the researchers wish to carry out new cohorts, which would make it possible to determine whether these biological markers could become diagnostic tools for Covid-long.
