Abnormal expression of alpha-galactosyl epitopes in man. A trigger for autoimmune processes?

Area of Science:

• Immunology
• Glycobiology
• Evolutionary Biology

Background:

• * The alpha-galactosyl epitope (Galα1-3Galβ1-4GlcNAc-R) is a key carbohydrate structure found on mammalian cell surface glycoconjugates.
• * In humans and Old World primates, expression of this epitope is absent due to low alpha-1,3-galactosyltransferase enzyme activity.
• * Approximately 1% of circulating IgG in humans comprises anti-Gal antibodies that specifically recognize this epitope.

Purpose of the Study:

• * To investigate the evolutionary significance of the alpha-galactosyl epitope and anti-Gal antibody interactions.
• * To explore the potential for an autoimmune response in humans if alpha-1,3-galactosyltransferase activity is restored.

Main Methods:

• * Analysis of carbohydrate structures on mammalian cell surfaces.
• * Examination of alpha-1,3-galactosyltransferase enzyme activity across different primate species.
• * Review of existing literature on anti-Gal antibody prevalence and function.

Main Results:

• * The alpha-galactosyl epitope is prevalent in non-primate mammals, prosimians, and New World monkeys.
• * Its absence in Old World monkeys, apes, and humans is linked to diminished alpha-1,3-galactosyltransferase activity.
• * The gene for alpha-1,3-galactosyltransferase appears to be present in the human genome.

Conclusions:

• * The evolutionary loss of the alpha-galactosyl epitope in humans may be a mechanism to avoid autoimmune reactions.
• * Reactivation of alpha-1,3-galactosyltransferase in human cells could lead to the synthesis of alpha-galactosyl epitopes.
• * This synthesis could potentially trigger an autoimmune response mediated by pre-existing anti-Gal antibodies.