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Fourteen patients examined in the study, published in the journal Immunity, showed wide-range immune responses.
However, the results of six of them who were evaluated two weeks after discharge suggest that the antibodies remained for at least that time.
The study also indicates which parts of the virus are most effective at triggering these immune responses, and should therefore be the target of possible vaccines.
The researchers, including those at Tsinghua University in China, noted that it is not clear why immune responses vary widely between patients.
This variability may be related to the initial amounts of virus the patients found, their physical states or their microbiota, they said.
Other open-ended questions, the researchers said, include whether these immune responses protect against Covid-19 in re-exposure to SARS-CoV-2, as well as which types of T cells are activated by infection with the virus.
It’s also important to note that laboratory tests used to detect antibodies to SARS-CoV-2 in humans still need additional validation to determine their accuracy and reliability, they said.
“These findings suggest that both B and T cells participate in immunomediated protection against viral infection,” said study co-author Chen Dong of Tsinghua University.
“Our work has provided a basis for further analysis of protective immunity and for understanding the mechanism behind the development of Covid-19, especially in severe cases. It also has implications for designing an effective vaccine to protect against infection,” Dong said. .
Relatively little is known about the protective immune responses induced by the disease-causing virus, SARS-CoV-2, and addressing this knowledge gap may accelerate the development of an effective vaccine, Cheng-Feng Qin from the Academy of Military Medical Sciences in China.
The researchers compared the immune responses of 14 Covid-19 patients who had recently become virus-free with those of six healthy donors.
Eight of the patients were recently discharged, and the remaining six were follow-up patients who were discharged two weeks before the analyzes.
The researchers collected blood samples and assessed levels of immunoglobulin M (IgM) antibodies, which are the first to appear in response to infection, as well as immunoglobulin G (IgG) antibodies, the most common type found in blood circulation.
Compared to healthy controls, both newly discharged and follow-up patients showed higher levels of IgM and IgG antibodies that bind to the nucleocapsid protein SARS-CoV-2, which encapsulates viral genomic RNA, as well as receptor S protein binding domain (S-RBD), which binds to receptors on host cells during the viral entry process.
These findings show that patients with Covid-19 can mount antibody responses to SARS-CoV-2 proteins and suggest that these antibodies remain for at least two weeks after discharge.
Five newly discharged patients had high concentrations of neutralizing antibodies that bind to a pseudovirus that expresses the SARS-CoV-2 S protein, the researchers said.
Neutralizing antibodies prevent infectious particles from interacting with host cells, they said.
All but one follow-up patient had detectable neutralizing antibodies against the pseudovirus, according to the researchers.
Compared to healthy controls, five newly discharged patients had higher concentrations of interferon gamma (IFN?)-Secreting T cells, a signaling molecule that plays a critical role in immunity, in response to the nucleocapsid protein of the SARS-CoV-2. said.
These are the same patients who had high concentrations of neutralizing antibodies, the researchers said.
