Cytokine storms may affect the severity of COVID-19 cases by lowering T cell counts, according to a new study published in Frontiers in Immunology.
Researchers studying coronavirus cases in China found that sick
patients had a significantly low number of T cells, a type of white
blood cell that plays a crucial role in immune response, and that T cell
counts were negatively correlated with case severity.
Interestingly, they also found a high concentration of cytokines, a
protein that normally helps fight off infection. Too many cytokines can
trigger an excessive inflammatory response known as a cytokine storm,
which causes the proteins to attack healthy cells. The study suggests
that coronavirus does not attack T cells directly, but rather triggers
the cytokine release, which then drives the depletion and exhaustion of T
cells.
The findings offer clues on how to target treatment for COVID-19,
which has become a worldwide pandemic and a widespread threat to human
health in the past few months. “We should pay more attention to T cell
counts and their function, rather than respiratory function of
patients,” says author Dr. Yongwen Chen
of Third Military Medical University in China, adding that “more
urgent, early intervention may be required in patients with low T
lymphocyte counts.”
Chen says he and his co-authors became interested in examining T
cells when they noticed that many of the patients they treated for
COVID-19 had abnormally low numbers of lymphocytes, a type of white
blood cell that includes T cells. “Considering T cells’ central role of
response against viral infections, especially in the early stage when
antibodies are not boosted yet, we took the T cells as our focal point,”
says Chen.
Authors examined 522 patients with coronavirus along with 40 healthy
controls. All patients studied were admitted to two hospitals in Wuhan,
China between December 2019 and January 2020, and ages ranged between 5
days and 97 years old. Of the 499 patients who had their lymphocytes
recorded, 76% had significantly low total T cell counts. ICU patients
had significantly lower T cell counts compared with non-ICU cases, and
patients over the age of 60 had the lowest number of T cells.
Importantly, the T cells that did survive were exhausted and could
not function at full capacity. Not only does this have implications for
COVID-19 patient outcomes, but T cell exhaustion leaves patients more
vulnerable to secondary infection and calls for scrupulous care.
Chen says that future research should focus on finding finer
subpopulations of T cells in order to discover their vulnerability and
effect in disease, along with identifying drugs that recover T cell
numbers and boost function.
Authors say that Tocilizumab is an existing drug that may be
effective, but that it needs to be investigated in the context of
coronavirus. Antiviral treatments, such as Remdesivir, may also prevent
the progression of T cell exhaustion, but all future treatments will
require further study.
In the meantime, this new research deepens our understanding of how
the novel coronavirus affects the body and it indicates ways to lessen
its impact.
https://www.eurekalert.org/pub_releases/2020-05/f-csa042320.php
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