Investigation of Specific IgG4 and IgE Antibodies to Cat Allergen Among 296 Subjects in the Project Viva Birth Cohort: Evidence that a Low Ratio of sIgG4:sIgE is a Significant Risk Factor for Asthma and Asthma Severity

We investigated IgE and IgG4 antibodies to cat allergen and asthma in the Viva Cohort at age 13 years to better understand the tolerance induced by living with a cat. ImmunoCAP assays for sIgE and sIgG4 used cut-offs of 0.84 and 70 ng/ml respectively. Values for sIgG4 to sIgE ratios were calculated for cases with positive results to both isotypes. Cat ownership in the last year was taken as high exposure. Moderate severe asthma (MSA) was defined as current asthma cases who reported two or more acute episodes in the last year. Full data was available for current asthma, MSA and cat exposure as well as specific sIgG4 and sIgE antibodies to cat extract for 296 subjects including 82 with current asthma. Among the 47 subjects with IgE to cat and a cat at home, the geometric mean ratio of sIgG4:sIgE among the 32 children without current asthma was 69.8 while the ratio for the 15 children with current asthma was 12.8 (p<0.01). Moreover, 10 of 13 subjects with asthma, who lived with a cat and had a slgG4:slgE ratio of less than 50, had MSA. In keeping with previous results, exposure to cat did not cause an increased prevalence of slgE to cat. However, among subjects with exposure to cat a ratio of slgG4: slgE lower than 50:1 was a significant predictor of current asthma and asthma severity. Our results suggest that children with a ratio of slgG4: sIgE less than 50:1 might benefit from cat specific intervention.