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. [ABSTRACT FROM AUTHOR]