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Infectious Diseases

Updated 06 May 2020

Blood count may offer clues to treatment of Covid-19

In a study, the majority of Covid-19 patients had significantly lower levels of T cells – a type of white blood cell that plays a crucial role in immune response against viral infections. What does this mean?

The severity of Covid-19 illness may be influenced by what researchers call "cytokine storms".

In a new study, investigators assessed 522 Covid-19 patients, aged five days to 97 years, who were admitted to two hospitals in Wuhan, China, in December and January. The study also included a "control group" of 40 healthy people.

Compared to the control group, 76% of Covid-19 patients had significantly lower levels of T cells – a type of white blood cell that plays a crucial role in immune response against viral infections.

Patients admitted to the intensive care unit had much lower T cell counts than those who didn't require ICU care. Patients over age 60 had the lowest T cell counts, the findings showed.

Loss and exhaustion of T cells

And the T cells that did survive in Covid-19 patients were exhausted and unable to function at full capacity, the study authors said.

Covid-19 patients also had high levels of cytokines – a protein that normally helps fight off infection. Too many cytokines can prompt an excessive inflammatory response called a "cytokine storm", which causes the proteins to attack healthy cells.

That suggests the new coronavirus does not attack T cells directly. Instead, it triggers the cytokine release, which results in the loss and exhaustion of T cells, according to the authors of the study published in the journal Frontiers in Immunology.

The study results provide new clues on how to treat Covid-19, the researchers said.

"We should pay more attention to T cell counts and their function, rather than respiratory function of patients," study author Dr Yongwen Chen of Third Military Medical University in Chongqing, China, said in a journal news release.

Chen added that "more urgent, early intervention may be required in patients with low T lymphocyte counts".

In addition, he noted, future research should focus on pinpointing subgroups of T cells that may be most important in Covid-19, along with identifying drugs that boost T cell counts and functioning.

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