Diagnosis of dog allergy in children : molecular assessment and refined characterization

Abstract

Dog allergy is a common cause of rhinitis and asthma in children, yet the diagnosis is a clinical challenge. Allergic sensitization, i.e. the presence of serum IgE antibodies, to dog dander affect up to 30 % of all children and adolescents, but not all sensitized children display symptoms. The most important diagnostic tool, the detection of IgE antibodies to dog dander extracts in serum does not reveal which allergen molecule in the extract that gives rise to the allergic sensitization and symptoms. Through molecular allergy diagnostics it is now possible to detect allergic sensitization to specific allergen molecules from dog, but the clinical relevance of sensitization to the different dog allergen molecules is not yet clear. When our investigations were initiated in 2014, there were six recognized dog allergen molecules, Can f 1- Can f 6, of whom Can f 1, Can f 2, Can f 4 and Can f 6 belong to the lipocalin protein family. Can f 3 is the dog serum albumin, and Can f 5 is the male dog allergen prostatic kallikrein.

The overall aim of this doctoral thesis was to improve diagnostics of dog allergy by identifying patterns of sensitization to dog allergen molecules associated with rhinitis and asthma in dog dander sensitized children and by exploring novel biomarkers and complementary diagnostic tests for dog allergy.

In paper I, we found that a positive nasal provocation test with dog dander extract was associated with an increasing number of positive sensitizations to dog allergen molecules and with sensitization to allergens from the lipocalin protein family. When investigating the impact of the different allergens, we found that sensitization to Can f 3, Can f 4 and Can f 6 conferred an increased risk for a positive vs a negative nasal challenge. On the contrary, monosensitization to Can f 5 was associated with a negative nasal provocation test. In paper II, we showed that the basophil activation tests to allergen molecules, evaluated by the basophil allergen threshold sensitivity (CD-sens), were positive in a majority of the sensitized children with a positive, as well as in those with a negative nasal provocation test. However, the levels of CD-sens to dog dander and to Can f 1 were higher in children with a positive nasal provocation. The levels of IgG or IgG4 to the investigated allergens did not differ between sensitized children with a positive and a negative nasal provocation test, while sensitized children with a dog at home had higher levels of IgG4 to Can f 1 and Can f 5 and lower CD-sens to all investigated allergen molecules. In paper III, we performed nasal transcriptomic analysis in dog dander sensitized children and healthy controls. The most over-expressed gene in dog dander sensitized children was CST1, coding for Cystatin 1. CST1 expression was enhanced in a cluster of children with lower FEV1, increased bronchial hyperreactivity, pronounced eosinophilia and higher CD-sens to dog compared with other dog dander sensitized children. Finally, in paper IV, we showed that asthma in dog dander sensitized children was associated with multisensitization to furry animal allergen molecules and to lipocalins. Children with severe asthma had higher IgE levels to the dog lipocalins Can f 2, Can f 4 and Can f 6 than other dog dander sensitized children. Moreover, severe asthma was associated with symptoms of dog allergy evaluated by nasal provocation testing.

In conclusion, we demonstrate that a detailed assessment using molecular allergy diagnostics may help clinicians to assess the impact of allergic sensitization on dog allergy and asthma morbidity. We found that multisensitization to dog allergens and sensitization to lipocalins is associated with dog allergy and that the analysis of CD sens, IgG4 antibodies and nasal gene expression may provide further information in the diagnosis of this common disease.