Patterns of immunoglobulin G responses to egg and peanut allergens are distinct: ovalbumin‐specific immunoglobulin responses are ubiquitous, but peanut‐specific immunoglobulin responses are up‐regulated in peanut allergy

Summary Background The clinical significance of food‐specific IgG subclasses in food allergy and tolerance remains unclear. Specific IgG titres are often reported in non‐standardized units, which do not allow comparisons between studies or allergens. Objective To quantify, in absolute units, ovalbumin (OVA)‐ and peanut‐specific IgG levels in children with peanut or egg allergy (active or resolved) and in non‐allergic controls. Methods Children aged 1–15 years were recruited. Peanut allergy was diagnosed by convincing history and a 95% predictive level of specific IgE; egg allergy or resolution was confirmed by oral challenge. Serum IgG, IgG1 and IgG4 levels (μg/mL) to OVA and peanut extract were quantified by ELISA. Results OVA‐ and peanut‐specific IgG was detected in all subjects. In non‐allergic controls ( n =18), OVA‐specific IgG levels were significantly higher than peanut‐specific IgG (median μg/mL IgG=15.9 vs. 2.2, IgG1=1.3 vs. 0.6, IgG4=7.9 vs. 0.7; P <0.01). There were no differences in OVA‐specific IgG, IgG1 and IgG4 between egg‐allergic ( n =40), egg‐resolved ( n =22) and control ( n =18) subjects. In contrast, peanut‐specific IgG (median μg/mL IgG=17.0, IgG1=3.3, IgG4=5.2) were significantly higher in peanut‐allergic subjects ( n =59) compared with controls and with non‐peanut‐sensitized but egg‐allergic subjects ( n =26). Overall, the range of IgG4 was greater than IgG1, and IgG4 was the dominant subclass in >60% of all subjects. Conclusion OVA‐specific IgG levels of egg‐allergic, egg‐resolved or control groups are not distinguishable. Higher peanut‐specific IgG levels are associated with clinical allergy, but the range of IgG titres of the allergic and control groups overlapped. Hence, OVA and peanut‐specific IgG measurements do not appear to be of diagnostic value. Strong IgG responses to OVA may be a normal physiological response to a protein frequently ingested from infancy, whereas up‐regulated IgG responses in peanut allergy may be indicative of a dysregulated immune response to peanut allergens.