Relationship of dog- and cat-specific IgE and IgG₄ levels to allergic symptoms on pet exposure

Background: Environmental allergens may induce the generation of allergen-specific IgE (sIgE) and IgG₄ (sIgG₄). Some studies report an association of sIgG₄ to protection against allergic symptoms after exposure to the relevant allergen. Objective: We examined the relationship of dog and cat sIgE and sIgG₄ levels to self-reported allergic symptoms on pet contact. Methods: Participants 18 years of age in the Detroit Childhood Allergy Study cohort were asked whether they experienced symptoms on exposure to cats and dogs. Serum was assayed for cat and dog sIgE and sIgG₄. Geometric means, ratios of cat and dog sIgE, sIgG₄, and ratios of sIgG₄/sIgE were compared between symptomatic and asymptomatic teens with the use of Wilcoxon rank sum tests. Ratios of sIgG₄/sIgE, adjusted for presence of sIgE (≥ 0.35 kU/mL), were analyzed with logistic regression. Results: Data on 500 participants were analyzed. Compared with asymptomatic teens, teens symptomatic with cat exposure had higher cat sIgE, sIgG₄, and lower ratio of sIgG₄/sIgE. Teens symptomatic after dog exposure had higher dog sIgE levels and lower sIgG₄/sIgE, but similar levels of sIgG₄ compared with asymptomatic participants. Increasing cat and dog sIgG₄/sIgE ratios were associated with a lower likelihood of reporting allergic symptoms (cat: adjusted odds ratio, 0.8; 95% CI, 0.6-0.9; dog: adjusted odds ratio, 0.8; 95% CI, 0.7-1.0). Conclusion: sIgG4 levels to cat and dog allergens correlate with lower rates of pet-induced allergic symptoms when interpreted in the context of concomitant sIgE. However, sIgG₄ appears to have little utility as an isolated marker to indicate that pet exposure will be well tolerated.