Airborne Particulate Matter and SARS-CoV-2 Partnership: Virus Hitchhiking, Stabilization and Immune Cell Targeting — A Hypothesis

It is widely assumed that the spread of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) infection in humans occurs through close contact with an infected person, short-range transmission through respirable droplets from an infected individuals' cough or sneeze, and aerosolized airborne droplets in long-range (over a few meters) transmission (1). Large respirable droplets (>5 μm) rapidly settle out of the air, whereas virus-laden small droplets (<5 μm), often referred to as “droplet nuclei” remain longer in the air and propagate depending on air-flow (1). Assuming that a fraction of aerosols remains infective, “droplet-nuclei” might contribute to airborne transmission of the virus, particularly in poorly ventilated and crowded indoor spaces. A recent commentary, and supported with >200 signatories, has further stressed the importance of inhalation exposure to viruses in respirable droplets at short to medium distances (up to several meters) (2).
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\nIn contrast to the inhalation mode of viral transmission through airborne respirable droplets, here we speculate an additional role for settled and airborne particulate matter (PM) not only in viral transmission through inhalation and ingestion, but also in promoting immunity through antigen delivery, adjuvanticity and trained immunity.