Cutaneous and serological responses to cat allergen in adults exposed or not to cats.

The relationship between pet ownership and the risk of developing respiratory allergic sensitization to pet allergens is still controversial. To determine the degree of cutaneous immediate hypersensitivity and the levels of specific IgE and IgG4 antibodies to cat allergen in cat sensitized patients directly or indirectly exposed to this animal. We studied 112 adolescents and adults sensitized to cat allergens (43 with and 69 without a cat at home). There were also 52 control subjects, 27 atopic non-sensitized to cat and 25 non-atopic. The degree of immediate hypersensitivity was assessed by using, in duplicate, skin prick test with four five-fold dilutions of cat hair allergen extract with the content of its major allergen Fel d 1 quantified in micrograms plus positive (10 mg/ml histamine chlorhydrate) and negative (saline solution) controls. The resulting wheal areas were analysed by means of Parallel Line Assay. A blood sample was collected from every patient and control subjects for the evaluation of serological cat specific IgE and IgG4 antibodies. Patients with cat at home had a lower cutaneous response than patients without this pet. The difference in the skin sensitivity was estimated in 3.4 times (P<0.01). There was no statistical difference between the levels of cat specific IgE antibodies in the two groups of patients (P=0.065). The levels of Fel d 1 specific IgG4 antibodies showed a statistically significant association with the presence of cat at home, with higher levels in patients owing cat at home than in patients without this pet (P<0.001). The results of this study demonstrate that direct cat exposure in adolescents and adults with respiratory allergy is associated with a lower cutaneous response to cat allergenic extract, assessed by SPT and compared with indirect exposure. In patients with cat at home mean levels of specific IgE are statistically comparable whereas the levels of IgG4 are higher in comparison with subjects not exposed to cats. The role of indirect exposure to cat allergens in airways sensitization also in adults is emphasized. Moreover, patients with cat at home show a cutaneous and serological sensitization to cat allergen not higher in comparison with subjects not exposed to cats.