Genetic and structural basis of the human anti-α-galactosyl antibody response

Humans lack the capacity to produce the Gal alpha 1-3Gal beta 1-4GlcNAc (alpha-gal) glycan, and produce anti-alpha-gal antibodies upon exposure to the carbohydrate on a diverse set of immunogens, including commensal gut bacteria, malaria parasites, cetuximab, and tick proteins. Here we use X-ray crystallographic analysis of antibodies from alpha-gal knockout mice and humans in complex with the glycan to reveal a common binding motif, centered on a germline-encoded tryptophan residue at Kabat position 33 (W33) of the complementarity-determining region of the variable heavy chain (CDRH1). Immunoglobulin sequencing of anti-alpha-gal B cells in healthy humans and tick-induced mammalian meat anaphylaxis patients revealed preferential use of heavy chain germline IGHV3-7, encoding W33, among an otherwise highly polyclonal antibody response. Antigen binding was critically dependent on the presence of the germline-encoded W33 residue for all of the analyzed antibodies; moreover, introduction of the W33 motif into naive IGHV3-23 antibody phage libraries enabled the rapid selection of alpha-gal binders. Our results outline structural and genetic factors that shape the human anti-alpha-galactosyl antibody response, and provide a framework for future therapeutics development.

Automated summary

Humans produce anti-alpha-gal antibodies in response to various immunogens, and this study reveals a common binding motif in these antibodies which is associated with a specific genetic factor. Additionally, the introduction of this binding motif into certain antibody libraries allows for the rapid selection of alpha-gal binders.