Immune system deviations determine differences between severe, mild cases of COVID-19

Editor's Note

This study led by researchers from the Stanford University School of Medicine finds that immunological deviations and lapses determine whether individuals get mild or severe cases of COVID-19.

The researchers analyzed the immune response in 76 patients with COVID-19 and in 69 healthy individuals. Most patients with severe COVID-19 had enhanced blood levels of proinflammatory cytokines. Three of these have been associated with lung inflammation in other diseases.

The researches also found elevated blood levels of bacterial debris, such as bacterial DNA and cell-wall materials in patients with severe cases of COVID-19. The more debris, the sicker the patient, and the more proinflammatory cytokines were found circulating in the blood. These findings suggest that bacterial products ordinarily present only in the GI system, lungs, and throat may make their way into the bloodsteam, launching enhanced inflammation that is spread throughout the body by the circulatory system.

In addition, the researchers found that the worse the case of COVID-19, the less effective cells of the innate immune system (ie, blood leukocytes) were in responding. Instead of being aroused by material from viruses and bacteria, these normally active cells remained sluggish.  

The study’s findings provide some insight into why some people develop severe cases of COVID-19 and others recover quickly, the researchers say.