Analysis of the intestinal microbiota in COVID-19 patients and its correlation with the inflammatory factor IL-18 and SARS-CoV-2-specific IgA

The current global COVID-19 pandemic is caused by beta coronavirus Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2), which already infected over 10 million and caused 500 thousand deaths by June 2020. Overproduction of cytokines triggered by COVID-19 infection, known as "cytokine storm", is a highly risk factor associated with disease severity. However, how COVID-19 infection induce cytokine storm is still largely unknown. Accumulating in vitro and in vivo evidence suggests that gut is also susceptible to COVID19 infection: Human intestinal organoids, an in vitro model which mimic the specific cell type and spatial structure of the intestine, were susceptible to SARS-CoV2 infection; A significant fraction of patients reported gut symptoms; Viral RNA may persist for more than 30 days and infectious virus could be isolated in fecal samples. The gastrointestinal tract is the primary site of interaction between the host immune system with symbiotic and pathogenic microorganisms. The bacteria resident in our gastrointestinal tract, known as gut microbiota, is important to maintain the homeostasis of our immune system. While imbalance of gut microbiota, or dysbiosis, is associated with multiple inflammation diseases5. It9s possible that SARS-CoV-2 infection may lead to alternation of gut microbiota thus worsen the host symptom. IL-18 is a proinflammatory cytokine produced multiple enteric cells, including intestinal epithelial cells (IECs), immune cells as well as enteric nervous system, and was shown to increase in the serum of COVID-19 patients. Immunoglobin A (IgA) is mainly produced in the mucosal surfaces, in humans 40-60mg kg-1 day-1 than all other immunoglobulin isotypes combined, and at least 80% of all plasma cells are located in the intestinal lamina propria. Recent study showed that SARS-CoV-2 specific IgA in the serum is positively correlate with the disease severity in COVID-19 patients11. Here we investigated the alterations of microbiota in COVID-19 patients, and its correlation with inflammatory factor IL-18 and SARS-CoV2 specific IgA.