New study suggests crucial role for lymphocytes in asymptomatic COVID-19 infection

Date:
October 14, 2020
Source:
American Society for Microbiology
Summary:
A retrospective study of 52 COVID-19 patients may help researchers
better understand why not everyone show symptoms of the disease. The
study's authors found that asymptomatic patients hosted viral loads
comparable to those of symptomatic patients, but 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.



FULL STORY ========================================================================== COVID-19 remains stubbornly inconsistent. More than a million people
have died and 35 million have been diagnosed, but a large fraction of
people infected with the coronavirus -- about 45%, according to recent estimates -- show no symptoms at all.


==========================================================================
A retrospective study of 52 COVID-19 patients, published this week in
mSphere, an open-access journal of the American Society for Microbiology,
may help researchers better understand why not everyone show symptoms
of the disease.

The study's authors found that asymptomatic patients hosted viral
loads comparable to those of symptomatic patients, but 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. Further analyses suggested
the interaction between the virus and the immune system likely played
a role in that process.

"Our findings suggested an important role for lymphocytes, especially
T cells, in controlling virus shedding," said virologist Yuchen Xia,
Ph.D., at Wuhan University's School of Basic Medical Sciences, in China,
who worked on the new study.

The wide range of COVID-19 symptoms is well documented. Asymptomatic
carriers, on the other hand, often go undiagnosed but can still shed the
virus and spread it to others. Understanding why some patients get sick
and others don't is one of the most important challenges in curbing the pandemic, Xia said. "They may cause a greater risk of virus transmission
than symptomatic patients, posing a major challenge to infection control."
Xia and his colleagues studied throat swabs and blood samples collected
from patients at Renmin Hospital of Wuhan University, including 27 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 used the throat
swabs to assess viral load, and on the blood samples they ran tests to
measure immunoglobins, cytokines, and immune cells.

Although both groups of patients had comparable viral loads, asymptomatic patients showed a statistically significant increase in number of CD4+
cells, white blood cells that fight infection, compared to symptomatic patients. Like previous studies, the new analysis also showed that
symptomatic patients were more likely to show impaired liver function
than asymptomatic patients. In contrast to other work, however, the new research did not find significant differences in cytokine levels between
the two groups.

Xia's group recently began collaborating on a larger follow-up study
with researchers in Germany, analyzing blood samples from more than
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.

Xia said he hopes this study will bring attention to the importance of including transmission from asymptomatic people in widespread efforts
to curb the pandemic. "More public health interventions and a broader
range of testing may be necessary to control COVID-19," he said.


========================================================================== Story Source: Materials provided by
American_Society_for_Microbiology. Note: Content may be edited for style
and length.


========================================================================== Journal Reference:
1. Huan Han, Zaichao Xu, Xiaoming Cheng, Youquan Zhong, Li Yuan, Fubing
Wang, Yan Li, Fang Liu, Yingan Jiang, Chengliang Zhu, Yuchen Xia.

Descriptive, Retrospective Study of the Clinical Characteristics
of Asymptomatic COVID-19 Patients. mSphere, 2020; 5 (5) DOI:
10.1128/ mSphere.00922-20 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/10/201014141034.htm

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