Mechanistic considerations linking SARS-CoV-2 infection, inflammation, and the loss of immune tolerance

The immune response to SARS-CoV-2 has been implicated in the onset of multiple, seemingly unrelated, autoimmune diseases. The immune response to SARS-CoV-2 has also been implicated in the unmasking and/or production of multiple autoantibodies, even in the absence of clinical disease. Despite such data, it remains unclear whether antibodies targeting antiviral signaling proteins and mitochondrial antigens reflect bystander activation or alternatively contribute to de novo viral immune escape mechanisms. With these comments in mind, a variety of professional antibody presenting cells and including lung resident macrophages of COVID-19 infected patients are impacted and dependent on the uptake of antibody-opsonized virus by Fcγ receptors; yet infection is aborted via antibody-dependent effector mechanisms or pyroptosis, possibly leading to autoantibody production, and autoinflammatory manifestations, respectively. TRIM21/Ro52, a cytosolic E3-ubiquitin ligase with an Fc-gamma receptor domain, functions as an intracytoplasmic antibody receptor, directs immune complexes binding virions but also autoantigens to autophagy. During autophagy, Ig-virions-TRIM21/Ro52-autoantigens complexes bind directly to class II human leukocyte antigen in lysosomal compartment, leading to subsequent presentation on the cell surface. This process favors the development of a specific humoral immune response but has the potential to lead to loss of tolerance. Interestingly, TRIM21/Ro52 can also contribute to pyroptosis. We propose that TRIM21/Ro52 is well-placed at the crossroad between the inflammatory response and clinical autoimmunity.