A team of researchers sought to fill the gaps in the understanding of immune memory after a SARS-CoV-2 infection. Their action led them to delve deeply into the patients’ immune factor response. To do this, the scientists measured several components of the immune system, including circulating antibodies, memory B cells and T cells specific to the new coronavirus, in patients with various levels of the disease, up to eight months after the infection.
The good news is that evidence of long-term immune memory has been found thanks to B cells.
There is immunity to COVID-19 in addition to antibodies
The collaborative team at the La Jolla Institute for Immunology (LJI) and the microbiology department at the Icahn School of Medicine in Mount Sinai studied the responses of immune cells and antibodies in more than 180 men and women who recovered from COVID-19.
As reported, the immune memory of these patients to the virus - in all types of immune cells studied - was measurable up to eight months after the onset of symptoms.
According to the authors, the results indicate "that durable immunity against secondary disease COVID-19 is a possibility in most individuals".
Our data show that immune memory in at least three immune compartments was measurable in ~ 95% of individuals five to eight months after the onset of symptoms.
The study authors wrote.
As the number of daily cases of COVID-19 worldwide continues to increase, whether an initial SARS-CoV-2 infection leads to long-term protective immunity against COVID-19 remains an issue.
The study of the nature of humoral response to the virus, which includes an antibody response, and the cellular immune response, which includes B cells and T cells, over periods of six months after the onset of symptoms could help inform the duration of protective immunity.
To this end, Jennifer Dan, a researcher at LJI, and her colleagues recruited more than 180 men and women from the United States who recovered from the disease. Most had had mild symptoms that did not require hospitalization, although 7% had been hospitalized.
Most subjects provided a blood sample at a single time, between six days and eight months after the onset of symptoms, although 43 samples were provided at six months or more after the onset of symptoms.
In 254 total samples from 188 COVID-19 cases, the team located antibodies, B cells, and two types of T cells. The antibody (IG G) for the Spike protein was relatively stable for more than 6 months and exhibited only modest declines six to eight months after the onset of symptoms.
Spike protein specific memory B cells were more abundant at six months than at one month after the onset of symptoms. T cells, however, showed only slight decay in the body. More specifically, SARS-CoV-2 specific CD4 + T cells and CD8 + T cells declined with a half-life of 3 to 5 months.
Although the authors caution that “direct conclusions about protective immunity cannot be made on the basis of [nas suas conclusões] because the protective immunity mechanisms against SARS-CoV-2 or COVID-19 are not defined in humans ”, they also say that several“ reasonable interpretations ”can be made from their study.
These include support for resting immune memory compartments, potentially contributing "in significant ways to protective immunity against pneumonia or severe secondary COVID-19," the researchers wrote.
The work is published on the Science portal in the newspaper “Immunological memory to SARS-CoV-2 assessed for up to eight months after infection“.