IGHE and allergic disease: In subjects with allergy only to cat, serum concentrations of specific IgE and IgG4 to cat dander but not to dog dander were higher than those in subjects without allergy to dog or cat (cat-specific IgE, 3.81 vs 0.62 kUA/L, P < 0.001; dog-specific IgG4, 0.60 vs 0.30 kUA/L, P < 0.05).