by Stanford University Medical Center

3D print of a spike protein of SARS-CoV-2, the virus that causes COVID-19–in front of a 3D print of a SARS-CoV-2 virus particle. The spike protein (foreground) enables the virus to enter and infect human cells. On the virus model, the virus surface (blue) is covered with spike proteins (red) that enable the virus to enter and infect human cells. Credit: NIH

ry sciences at the University of Hong Kong.

Three molecular suspects

The researchers analyzed the immune response in 76 people with COVID-19 and in 69 healthy people. They found enhanced levels of molecules that promote inflammation in the blood of severely ill COVID-19 patients. Three of the molecules they identified have been shown to be associated with lung inflammation in other diseases but had not been shown previously in COVID-19 infections.

“These three molecules and their receptors could represent attractive therapeutic targets in combating COVID-19,” said Pulendran, who is the Violetta L. Horton Professor. His lab is now testing the therapeutic potential of blocking these molecules in animal models of COVID-19.

Bacterial debris and immune paralysis

The scientists also found elevated levels of bacterial debris, such as bacterial DNA and cell-wall materials, in the blood of those COVID-19 patients with severe cases. The more debris, the sicker the patient—and the more pro-inflammatory substances circulating in his or her blood.

The findings suggest that in cases of severe COVID-19, bacterial products ordinarily present only in places such as the gut, lungs and throat may make their way into the bloodstream, kick-starting enhanced inflammation that is conveyed to all points via the circulatory system.

But the study also revealed that, paradoxically, key cells of the innate immune system in the blood of COVID-19 patients became increasingly paralyzed as the disease got worse. Instead of being aroused by the presence of viruses or bacteria, these normally vigilant cells remained functionally sluggish.

If high blood levels of inflammation-promoting molecules set COVID-19 patients apart from those with milder cases, but blood cells are not producing these molecules, where do they come from? Pulendran believes they originate in tissues somewhere in the body—most likely patients’ lungs, the site of infection.

“One of the great mysteries of COVID-19 infections has been that some people develop severe disease, while others seem to recover quickly,” Pulendran said. “Now we have some insights into why that happens.”

Pulendran is a member of Stanford Bio-X and a faculty fellow of Stanford ChEM-H.

Explore further

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More information: Systems biological assessment of immunity to mild versus severe COVID-19 infection in humans, Science 11 Aug 2020: eabc6261, DOI: 10.1126/science.abc6261 , science.sciencemag.org/content … 8/10/science.abc6261
Journal information: Science
Provided by Stanford University Medical Center