How blood group A evolution involves reduced innate immunity and doubles the host's exposure to pathogens, as suggested by SARS-CoV-2 (COVID-19) infection. — Brief communication —

The formation of evolutionary hybrid Tn (T “nouvelle”) cross-reactive A antigens, together with glycosylations on cell surfaces and plasma proteins, and the generation of mucin-type A- and B allele-connected hybrid epitopes, doubles the host's exposure to pathogens by two genetically distinct bindings, neutralising the innate anti-Tn/A reactivities of pre-existing polyreactive IgM. This consequent protection against A-phenotypic autoimmunity implies a reduction in innate immunity, which explains the increased susceptibility and severity of disease in blood group A individuals.