Fel d 1-specific IgG antibodies induced by natural exposure have blocking activity in skin tests.

Cat-allergic patients frequently have IgG antibodies directed against Fel d 1. The aim of this study was to investigate whether these IgG antibodies influence the results of the skin test. Titrated skin tests were performed with Fel d 1 and IgE and IgG antibody levels were measured in 59 patients with cat allergy. Levels of specific IgG against Fel d 1 ranged from less than 0.25 to 3.5 microgram/ml. By means of a multiple regression analysis it was shown that the amount of specific IgG antibodies contributes significantly to the results of the skin test. Presence of specific IgG against Fel d 1 was accompanied by higher skin thresholds for Fel d 1. In conclusion, this study indicates that even low levels of specific IgG, induced by natural exposure to cat allergens, have a blocking effect on the early phase skin reaction.