Paleo-immunology of human anti-carbohydrate antibodies preventing primate extinctions.

Two human natural anti-carbohydrate antibodies appeared in critical evolutionary events that brought primates and hominins to brink of extinction. The first is the anti-Gal antibody, produced in Old-World monkeys (OWM), apes and humans. It binds the carbohydrate-antigen 'α-gal epitope' (Galα1-3Galβ1-4GlcNAc-R) on carbohydrate-chains (glycans) synthesized by non-primate mammals, lemurs and New-World monkeys (NWM). The second is anti-N-glycolylneuraminic-acid (anti-Neu5Gc) antibody binding Neu5Gc on glycans synthesized by OWM, apes and most non-primate mammals. Ancestral OWM and apes synthesized α-gal epitopes and were eliminated ~20-30 million-years-ago (mya). Only few accidentally mutated offspring lacking α-gal epitopes, produced anti-Gal and survived. Hominin-populations living ~3 mya synthesized Neu5Gc and were eliminated, but few mutated offspring that accidently lost their ability to synthesize Neu5Gc, produced natural anti-Neu5Gc antibody. These hominins survived and ultimately evolved into present-day humans. It is argued that these two near-extinction events were likely to be the result of epidemics caused by highly virulent and lethal enveloped viruses that killed parental-populations. These viruses presented α-gal epitopes or Neu5Gc synthesized in host-cells of the parental-populations. Mutated offspring survived the epidemics because they were protected from the lethal virus by the natural anti-Gal or anti-Neu5Gc antibodies they produced due to loss of immune-tolerance to α-gal epitopes or to Neu5Gc, respectively.