De novo natural anti-M alloantibody emergence in severe Coronavirus Disease 2019.

The immune response is a key player in the course of SARS-CoV-2 infection, and is often seriously dysfunctional in severe Coronavirus Disease 2019. The hyperinflammatory status has been described to be accompanied by the appearance of autoantibodies. In a lethal COVID-19 infection, we observed the emergence of a de novo natural alloantibody which targeted the M antigen from the MNS blood group on red blood cells (RBC) without evidence of any cross-reaction with SARS-CoV-2 antigens.