Researchers conducted a retrospective study of 52 coronavirus patients to compare the development of infection in symptomatic Covid-19 patients with asymptomatic patients.
The study found that both the patients hosted the same amount of viral load. However, asymptomatic patients showed higher levels of lymphocytes (a type of white blood cell responsible for immune responses), cleared the viral particles faster, and had lower risks of long-term complications.
The study was published in mSphere, an open-access journal of the American Society for Microbiology.
Further examination revealed the interaction between the virus and the immune system likely played a role in that process.
Author of the study, Virologist Yuchen Xia, Ph.D., at Wuhan University’s School of Basic Medical Sciences, in China, said in a statement: “Our findings suggested an important role for lymphocytes, especially T cells, in controlling virus shedding.”
Xia mentioned that symptoms of the coronavirus are well-observed. However, when it comes to asymptomatic carriers, they often go unobserved and undiagnosed but can still shed the virus and spread it to others.
Hence, understanding why some patients get sick and others don’t is one of the most critical challenges in curbing the pandemic, Xia said.
For the study, Xia and his colleagues analyzed throat swabs and blood samples collected from patients at Renmin Hospital of Wuhan University. This included 27 patients who had been admitted for complications related to Covid-19 and 25 asymptomatic patients who had been admitted for other reasons but tested positive for the SARS-CoV-2 virus upon arrival.
The researchers tested the viral load and took the blood samples to measure immunoglobins, cytokines, and immune cells.
The findings suggested that both groups had comparable viral loads. However, asymptomatic patients showed a statistically significant increase in the number of CD4+ cells, white blood cells that fight infection, compared to symptomatic patients.
The new analysis supported previous studies by showing that symptomatic patients were more likely to show impaired liver function than asymptomatic patients.
However, in contrast to other studies, the new study did not find significant differences in cytokine levels between the two groups.
Xia’s group has now collaborated with researchers in Germany to analyzing blood samples from over 100 patients with severe Covid-19 symptoms and 30 patients with mild symptoms.
They also plan to conduct animal studies to better understand the role of T cells in viral shedding.