Contact between the host and SARS-CoV-2 results in activation of the host's transmembrane protease serine subtype 2 (TMPRSS2) and ontogenetic polypeptide GalNAc transferase, performing formation of a cross-species molecular O-glycan bridge. Thus, formation of a hybrid Tn/A-like antigen, should play a key role in SARS-CoV-2 infection, while the pre-existing innate anti-Tn/A-reactive immunoglobulin M (IgM) provides the first line of defense. The hybrid Tn/A-like antigen signifies host-mediated

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... igenicity, or host-specific foreignness that replaces the syngeneic Tn/A, which becomes the target of infection and in the human blood group O(H) will be recognized as non-self by the pre-existing innate anti-Tn/A-reactive IgM. In blood group A this activity is neutralized or reduced by A-allelic, phenotypic glycosylation, while the virus gets attached to the cell surface by the same enzymatic step and enters the cell via established pathways.