Monoclonal antibodies to the major feline allergen Fel d I. I. Serologic and biologic activity of affinity-purified Fel d I and of Fel d I-depleted extract.

Monoclonal antibodies were raised against a major feline allergen, Fel d I. The specificity of the antibodies for Fel d I was demonstrated by a modified crossed immunoelectrophoretic procedure. These antibodies were used in affinity purification and depletion. Fed d I was eluted from the affinity matrix at a low pH. It was tested in serologic and biologic assays. Results of both the RAST and the histamine release test with affinity-purified Fel d I confirmed that it is a very potent allergen for the majority of patients allergic to cats. In the extract depleted with the monoclonal antibody, the ratio Fel d I/cat albumin was reduced by a factor of 20. With this depleted extract, 18 of 25 patients showed a reduction greater than 50% of the bound anti-IgE in the RAST compared with the RAST with crude cat extract. In the histamine release test with cells from two patients, the activity of the depleted extract was reduced by factors of 30 and 40, respectively. Depletion of Fel d I by polyclonal antibodies resulted in a reduction of the ratio Fel d I/cat albumin by a factor of 330. In the RAST, a reduction of the IgE response greater than 50% was found in 23 of 25 patients; in 12 patients the reduction was greater than 90%. In the histamine release test, the polyclonally depleted extract was 200 to 300 times less potent than the crude cat-dander extract. These results indicate that a very large proportion of the allergenic activity of cat-dander extract is caused by a single molecule: Fel d I.