Immunotherapy for cat asthma

In 22 patients with cat asthma who were highly sensitive to cat, we compared, double-blind, the effects of immunotherapy with cat-hair and dander extract (11 patients) with effects of placebo (11 patients). Patients were matched by the dose of the cat extract expressed in Food and Drug Administration (FDA) units of Fel d I (previously called cat allergen 1) required for end point reaction in intradermal skin test end point titration (STEPT), for in vitro leukocyte histamine release (LHR), and for the dose of cat extract producing a 20% fall in FEV1 (cat-extract PD20) in bronchoprovocation test. Patients were matched also for bronchoprovocation dose of methacholine producing a 20% fall in FEV1 (methacholine PD20). Patients were randomly assigned to one of two treatment groups. During immunotherapy, doses were increased to maintenance dose of 4.56 FDA units of Fel d I, or, if this were less, to the highest tolerated dose. Systemic reactions to cat-extract immunotherapy were mild and infrequent. Before and during immunotherapy, we measured (in FDA units of Fel d I) cat-extract PD20, cat-extract intradermal STEPT, cat-extract in vitro LHR, serum levels of cat IgG and cat IgE, and methacholine PD20. After they had received 1 year of immunotherapy, patients receiving cat extract, in comparison to patients receiving placebo, had decreased cat-extract PD20 (p less than 0.01), diminished responses to cat-extract intradermal STEPT (p less than 0.025), increased IgE antibodies toward cat extract (p less than 0.01), increased IgG antibodies toward cat extract, Fel d I, and cat albumin (p less than 0.001), but no significant change in cat-extract in vitro LHR or in methacholine PD20. We conclude that cat-extract immunotherapy was well tolerated, significantly decreased skin and bronchial responses to cat extract, and significantly increased IgE antibodies to cat extract and IgG antibodies to cat extract, Fel d I, and cat albumin.