Immunity from the virus may be more extensive than is believed. An innovative method, using strong neutralizing antibodies, is raising hope.
As the intensity of the pandemic fades in Europe, continues in the United States, is in full swing in Latin America and seems to be rebounding in Asia, the question of immunity conferred on the 8 million people worldwide , have survived to this day after contracting the Covid-19 (450,000 have died) becomes a major subject: how long will they be protected? Can they be contaminated again? What type of protection should a vaccine target?
There are two main immunities: innate and adaptive. The year is a first line of defense where physical (skin, mucous membranes), chemical (secretions, mucus) barriers intervene, infantry cells (macrophages, neutrophilic white blood cells), which will fight the aggressor, so-called dendritic cells, which have the role of perfectly identifying it in case it returns, and small proteins (cytokines) which stimulate the immune troops. The adaptive is what interests us here. Its role is to protect the organism if the enemy attacks it again. It takes two complementary forms: humoral and cellular. 1. The humoral produces antibodies (immunoglobulins) which neutralize the aggressor from white blood cells called B lymphocytes. 2. The cellular form involves other white blood cells, T lymphocytes, which can be cytotoxic (CD8 +) , that is to say killers, their mission being to destroy the infected cells, or regulators (CD4 +), which coordinate and direct the attacks of CD8 +.
Antibodies linked to the SARS-CoV pandemic have persisted for almost 3 years
In humans, adaptive immunity after infection with a coronavirus is quite variable: the antibodies linked to the SARS-CoV pandemic in 2002-2004, very aggressive but of low magnitude (8,096 infected in thirty countries, 774 deaths) persisted for approximately three years in survivors. Antibodies linked to coronaviruses responsible for mild colds persist only for a few months. Antibodies linked to Covid-19 appear to become weakly neutralizing after a delay varying from three weeks to three months. Serological tests, whose reliability is far from perfect (there are many false negatives), only concern humoral immunity (presence or absence of antibodies).
What about cellular immunity?
Three American teams affiliated with the United States Federal Agency for Public Health (Centers for Disease Control and Prevention) detected, in 20 adults Covid-19 positive, not hospitalized and whose blood samples were studied 20 to 35 days after the onset of symptoms, the presence of CD8 + and an important CD4 + response directed 50% against the protein Spike, which allows the virus to enter cells, and 50% against other of its antigens. This is a very significant cellular immunity. It could be more durable than humor. Another good news: on samples of healthy subjects collected between 2015 and 2018, well before the emergence of Covid-19, the same researchers discovered that half of them had CD4 + also directed against the Spike of Sars-CoV -2. This suggests the existence of crossed immunities, so that old infections, with common coronavirus (simple colds), could protect a significant part of the population against the current virus. Hence also the possibility that group immunity, a factor which disables epidemics, may be achieved more quickly than expected.
What to think of the risk of short-term recontamination? There is much talk of it, but no tangible evidence supports this thesis for the moment. As for the question: “Can Covid-19 remain latent in the body in cell reservoirs?” The answer is “no”, because that fact is that of DNA viruses, while our public enemy is an RNA virus.
Hope for powerful neutralizing monoclonal antibodies
Using an innovative method that has made it possible to genetically analyze B lymphocytes from 60 patients healed from Covid-19, the team of Professor Sunney Xie, renowned Sino-American chemist, director of the Center for Advanced Genomic Innovation at Peking University, was able to identify 14 antibodies which neutralize the ACE2 receptor, targeted by the virus to penetrate human cells. One of them, the very powerful BD-368-2, injected into infected mice, reduces 2,500 times the viral load! Administered to normal mice, it protects them from the Covid-19. Human studies will begin.
Also read.No significant transmission of Covid-19 between children, confirms Pasteur
Pending (twelve to eighteen months) a vaccine conferring humoral or cellular immunity or both, this monoclonal antibody could be produced on a large scale, available next winter and given as a preventive and curative! It is better than injecting plasma from cured subjects, which seems to work but is not a technique applicable everywhere.
Any reproduction prohibited–
