Thread by @sciencescanner

This is interesting (to me at least) because it’s an effect we predicted almost 20 years ago now

Following thread explains exactly why this is what you’d expect

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(H/T @manal_mehta)

https://twitter.com/johnnosta/status/1240392418366717956

ABO blood groups are caused by different sugar groups that decorate the outside of your red blood cells. A and B have extra sugars (called fucose) on them, which are missing in group O

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The A blood group antigen structureky resembles another sugar group called “alpha-gal” that humans lack but every other species possesses (because we deleted the enzyme alpha-galactosyl transferase) very early in Hunan evolution

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We published in the late 90s that everyone has natural antibodies to alpha-gal as a result (because it’s foreign to us but present everywhere in our environment) - and we predicted that these antibodies played an important role as first-line defence vs infection

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We then found that people with A blood group have much lower levels of anti-alpha gal natural antibodies, particularly IgG2 class. Why? Because anti-alpha gal cross-reacts to A blood group antigen - so gets deleted in early life in A individuals to prevent autoimmunity

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We proposed that O blood group was therefore a positively-selected trait with a survival advantage versus A under high infectious load. And now #COVID19 is showing us that effect in action

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The effect isn’t binary (O people still can get disease) but the level of thus front-line protection will reduce the apparent dose of virus received when exposed - so “left shift” the severity curve

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This may explain why intrzvenous immunoglobulin (IVIG) from non-immune people still helps. And I assume they produce IVIG from O (universal) donors always to prevent anti-red cell effects... so highest level of protective anti-alpha gal

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May also explain geographical variations in infectious spread and rates of severe symptoms because different populations have very different distributions of ABO blood groups due to founder effects

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Finally the kicker: fascinating science but hard to see how to leverage this knowledge to improve safety or treatment on the ground

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For anyone interested here is our first discovery of these natural anti-alpha gal antibodies: pubmed.ncbi.nlm.nih.gov/10493920/?from…