IgE production to α-gal is accompanied by elevated levels of specific IgG1 antibodies and low amounts of IgE to blood group B

Abstract

IgE antibodies to gal-α-1,3-gal-β-1,4-GlcNAc (α-gal) can mediate a novel form of delayed anaphylaxis to red meat. Although IgG antibodies to α-gal (anti-α-gal or anti-Gal) are widely expressed in humans, IgE anti-α-gal is not. We explored the relationship between the IgG and IgE responses to both α-gal and the related blood group B antigen. Contradicting previous reports, antibodies to α-gal were found to be significantly less abundant in individuals with blood group B or AB. Importantly, we established a connection between IgE and IgG responses to α-gal: elevated titers of IgG anti-α-gal were found in IgE-positive subjects. In particular, proportionally more IgG1 anti-α-gal was found in IgE-positive subjects against a background of IgG2 production specific for α-gal. Thus, two types of immune response to α-gal epitopes can be distinguished: a 'typical' IgG2 response, presumably in response to gut bacteria, and an 'atypical', Th2-like response leading to IgG1 and IgE in addition to IgG2. These results suggest that IgE to a carbohydrate antigen can be formed (probably as part of a glycoprotein or glycolipid) even against a background of bacterial immune stimulation with essentially the same antigen.

Figure 1. IgG responses to α-gal and blood group B antigens.

A) Schematic representations of gal-α-1,3-gal-β-1,4-GlcNAc (α-gal), gal-α-1,3-gal (gal2) and blood group B (B) antigens. B) IgG anti-α-gal, anti-gal2, and anti-B in B⁺ and B^– individuals, as measured in ELISA (1 µl serum/test). Bars represent median and interquartile ranges. B^– individuals make significantly more IgG to all three antigens (Mann-Whitney; ** p<0.01; *** p<0.001). C) Correlations between IgG anti-α-gal and IgG anti-gal2 (Spearman r = 0.83; p<0.0001), IgG anti-α-gal and IgG anti-B (r = 0.59; p = 0.009), and IgG anti-gal2 and IgG anti-B (r = 0.58; p = 0.0011). Light-colored dots correspond to B⁺ subjects. None of the sera contained detectable amounts of IgE anti-α-gal.

Figure 2. Individuals positive for IgE anti-α-gal make significantly more IgG anti-α-gal.

IgG antibody responses to A) α-gal, B) gal2, and C) B antigens in individuals who are positive for IgE anti-α-gal (IgE⁺), and individuals from both Virginia, USA, and North-Holland, The Netherlands, who are negative for IgE anti-α-gal (IgE^–), as measured in ELISA (1 µl serum/test). All subjects are B^–. IgE⁺ individuals make significantly more IgG anti-α-gal and anti-gal2, but not anti-B (Kruskal-Wallis with Dunn’s multiple comparison test). NS: not significant.

Figure 3. Correlations of IgG and IgE antibody responses in subjects positive for IgE anti-α-gal.

A) IgG anti-α-gal, anti-gal2, and anti-B in IgE⁺ subjects (0.3 µl serum/test), including two B⁺ cases. B) Correlations between IgG anti-α-gal and IgG anti-gal2 (Spearman r = 0.76; p<0.0001), IgG anti-α-gal and IgG anti-B (r = 0.48; p = 0.048), and IgG anti-gal2 and IgG anti-B (r = 0.53; p = 0.021). Light-colored dots correspond to B⁺ subjects. C) IgE anti-α-gal and anti-B measured in IgE radioimmunoassay. Median responses were 21.7 (IQR 9.9–47.5) IU/ml for IgE anti-α-gal, and 1.3 (IQR 0.3–3.6) IU/ml for IgE anti-B, which is significantly lower (p<0.0001). Levels are nevertheless correlated (r = 0.76; p = 0.0003).

Figure 4. IgG subclasses to α-gal, gal2, and B antigens in IgE⁺ and IgE^– individuals.

Contribution of A) IgG1 and B) IgG2 antibodies to α-gal, gal2, and B antigens in IgE⁺ and IgE^– individuals from both Virginia and North-Holland. Bars represent median and interquartile ranges. IgE⁺ individuals make significantly more IgG1 to all three antigens (Mann-Whitney; * p<0.05; ** p<0.01; *** p<0.001).