SARS-CoV-2-Immune-Microbiome Interaction: Lessons from Respiratory Viral Infections.

By the beginning of 2020, the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection has rapidly evolved into an emergent worldwide pandemic, an outbreak whose unprecedented consequences highlighted the existing flaws within the global public healthcare systems. While the coronavirus disease 2019 (COVID-19) is bestowed with a broad spectrum of clinical manifestation involving vital organs, the respiratory system transpires as the main route of entry of SARS-CoV-2, with the lungs being its primary target. Of those infected, up to 20% require hospitalization on account of severity, while the majority of patients are either asymptomatic or exhibit mild symptoms. Exacerbation in disease severity and complications of COVID-19 infection have been allied with multiple comorbidities including hypertension, diabetes mellitus, cardiovascular disorders, cancer, and chronic lung disease. Interestingly, a recent body of evidence have foregrounded the pulmonary and gut microbiome as potential modulators in altering the course of COVID-19, plausibly via the microbiome-immune system axis. While relative concordance between microbes and immunity is still not fully elucidated in a COVID-19 disease context, we present here an overview of our current understanding of this COVID-19-microbiome-immune cross talk and discuss the potential contributions of microbiome-related immunity to SARS-CoV-2 pathogenesis and COVID-19 disease progression.