Quantitative Binding Assay for Measuring Specific IgG Antibodies to Alpha-Gal Using the Neoglycoprotein Gal-α-1,3-Gal-β-1,4-Glcnac-Human Serum Albumin

Abstract

Tick bites are known to induce IgE production to alpha-gal. Elevated alpha-gal IgG1 compared to natural alpha-gal IgG2 production has been reported in alpha-gal IgE+ subjects. We here report further investigation of the relationship between alpha-gal IgG and both reactions to red meat and exposure to ticks. Methods: IgG from serum was absorbed onto recombinant Protein G-Sepharose and incubated with radiolabeled allergen. The radioactivity of bound allergen was measured using a gamma counter. A control curve was generated in parallel to assign unitage. Additional testing of serum immunoglobulins was performed via ImmunoCAP and nephelometry. Results: Alpha-gal IgG was measured in a Northern Sweden cohort and in subjects presenting to allergy clinics in Virginia with delayed reactions to red meat. Alpha-gal IgG was significantly higher in alpha-gal IgE+ subjects versus alpha-gal IgE- subjects, and longitudinal serology in several alpha-gal IgE+ subjects demonstrates parallel alpha-gal IgE and IgG response trends. Among the alpha-gal IgE+ subjects, alpha-gal IgG was higher in those with alpha-gal IgE:total IgE ratios >25%, but was not related to reported severity to red meat. Compared to the alpha-gal IgE- subjects in Virginia, alpha-gal IgG was lower in the group from Northern Sweden, where alpha-gal IgE-mediated hypersensitivity is absent and ticks are rare. Conclusions: Alpha-gal IgG is strongly related to alpha-gal IgE and is significantly lower in prevalence and titer in subjects without tick exposure. The absence of a relationship between alpha-gal IgG and severity of reactions to red meat suggests that the alpha-gal syndrome may not be a suitable candidate for conventional immunotherapy.