Covid-19, for vaccines the role of mucous membranes should not be underestimated

Covid-19, for vaccines the role of mucous membranes should not be underestimated

Two research groups have observed that an important part of the immune response that occurs immediately after infection is given by certain antibodies, the IgA immunoglobulins. These are found both in the blood and in an important way on the mucous membranes

(photo: Getty Images) What characteristics should an effective and useful vaccine have in preventing Covid-19 and in fighting the pandemic? A hypothesis not yet widely explored is that of considering the production of particular antibodies, IgA immunoglobulins, which have so far remained in the shadow of their IgG companions. The result is the result of two different studies published in Science Translational Medicine. The research analyzed the immune system response against the new coronavirus in people already infected as a starting point for finding new avenues of research and potentially design for new vaccines. In both studies, one from the Sorbonne University and Inserm (French National Institute for Research on Health and Medicine) and the other from The Rockefeller University in New York, the researchers found that much of the immunity that appears immediately after infection - not so much in the long term, therefore, it is supported by IgA, rather than by IgG immunoglobulins (which however remain central).

Antibodies: IgG and IgM

A good vaccine must undoubtedly produce a substantial antibody response, that is specific antibodies directed against Sars-Cov-2. In general, when contagion occurs, the immune system is usually activated by gradually deploying new components to counter the infection. To intervene first in contact with an unknown and potentially pathogenic organism, and to appear in the blood, are the immunoglobulin M (IgM), which has often been discussed in relation to serological tests to measure both IgM and IgG.

Only after the IgG arrive and having them positive in patients with Covid-19 can indicate that the infection is still ongoing or even that it has ended. These immunoglobulins represent 75% of the antibodies in the blood and are the pivot of secondary immune responses, ie they are relevant to contacts with the virus after the first (against reinfections) and their production is the goal of vaccines.

The role of IgA

Another response, which is sometimes not paid enough attention, is given by immunoglobulin A (IgA). One of the first barriers placed on the mucous membranes and in external secretions, which prevents viruses and other pathogens from entering our body and giving rise to a substantial infection, are precisely the IgA immunoglobulins.

Lo French study

The researchers measured in patients with Covid-19 both the levels of all these antibodies in the blood, saliva and secretions, and the increase in B lymphocytes, at the basis of the production of the aforementioned antibodies and so-called humoral immunity - then there is another slice of acquired immunity, that given by T lymphocytes, called cellular immunity. In the study signed by the university the Sorbonne and Inserm and colleagues, first signed by Delphine Sterlin, the researchers observed that once the contact between the Sars-Cov-2 and the cells (in already infected patients) have the immune system response is significantly more IgA immunoglobulins than other immunoglobulins. IgA in the blood rapidly decreases one month after infection, even if the neutralizing IgA antibodies remain in the saliva for up to 73 days after Covid begins, thus more than two months.

The role of 'mucosal immunity

The second study, first signed by Zijun Wang, the authors arrive at similar conclusions. In this case, scientists show that in a particular double formula (dimeric, in which two identical molecular components form a single molecular entity), as found in the nose and pharynx, IgA is well 15 times more potent than the same immunoglobulins in the form single (monomeric), present in the blood. For this reason, in addition to the central role of IgG, the role of IgA and immunity linked to mucous membranes should be investigated, according to the authors, also in view of the development of new vaccines against the coronavirus. "These results provide an essential element of observation on the basis of the data that emerged regarding the types of antibodies associated with optimal protection against a second infection", the study reads, "and it must be considered that a vaccination regimen with the aim targeting precisely these antibodies could provide a powerful yet short-lived response ".

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