The body’s protective antibodies against the new coronavirus target the second part of the virus in more severe cases of COVID-19 than in milder forms of the disease and have significantly disappeared within months of infection, new research says.
According to scientists, including those from Stanford University in the USA, the findings shed new light on the connections between the course of the disease and the patient’s immune response.
A study published in the journal Science Immunology found that people with severe COVID-19 have lower levels of antibodies that target the spike protein that the virus uses to enter human cells than those that target the inner shell proteins of the SARS-CoV-2 virus.
“This is one of the most comprehensive studies of the immune response of antibodies to SARS-CoV-2 in humans across the spectrum of disease severity, from asymptomatic to fatal,” said Scott Boyd, co-author of the study from Stanford University. “We assessed multiple time points and sample types, and we also analyzed viral RNA levels in patient nasopharyngeal swabs and blood samples. It’s one of the first big glimpses of this disease, ”Boyd said.
In the study, the researchers studied 254 people with asymptomatic, mild or severe COVID-19 who were identified by either routine testing or screening for occupational health at Stanford Health Care or who came to the Stanford Health Care Clinic with symptoms of COVID-19. According to the scientists, 25 people with symptoms were treated as outpatients, 42 were hospitalized outside the intensive care unit, and 37 were treated in the intensive care unit.
The study noted that 25 people in the study died from the disease.
From the analysis of patient samples, the scientists said that antibodies that recognize and bind to the protein spike prevent the virus from infecting cells. However, they said that antibodies that recognize other viral components are unlikely to prevent the virus from spreading. The researchers assessed the levels of three types of antibodies – IgG, IgM and IgA – in the patients. They assessed the proportions of antibodies that target the viral spike protein or the inner shell of the virus as the disease progressed and patients recovered or became increasingly ill.
“We found that disease severity correlated with the ratio of antibodies recognized by protein class domains compared to other unprotected viral targets,” Boyd said. “Those people with mild disease had a higher proportion of antibodies against the spikes, and those who died from their disease had more antibodies that recognized other parts of the virus,” he added.
Although the study identified trends among a group of patients, the researchers said there was still significant variability in the immune response conducted by individual patients, especially those with severe disease.
They believe that antibody responses are unlikely to be the only determinant of one’s outcome. “Among people with a serious illness, some die and some recover. Some of these patients react strongly, while others have a more moderate response, ”Boyd said.
“So a lot of other things are happening. Other branches of the immune system are also involved. It is important to note that our results identify correlations, but do not prove causality, ”he added.
The researchers also found that people with asymptomatic and mild diseases had overall lower levels of antibodies than those with serious illness. IgM and IgA levels consistently decreased in patients after recovery to low or undetected levels for a period of about one to four months after the onset of symptoms, and IgG levels dropped significantly.
“This is quite in line with what has been seen with other coronaviruses that regularly circulate in our communities to cause colds,” Boyd said.
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