Circulating cat allergen and immune complexes in cat-allergic children

Background The first encounters with allergens seem to influence the develo pment of allergy. Food antigens have been detected in sera as free antigens and in complexes with IgG but less is known about the presence of inhalant allergens. Objective To investigate the presence of the major cat allergen Fel d 1, ei ther as free allergen and/or in complexes with IgG and IgE antibodies in se ra from atopic children. Methods Serum samples from 33 cat allergic asthmatic children, 7-17 years o ld, and 15 non-allergic controls were investigated for the presence of Fel d 1 by ELISA (detection limit 0.13 mu g/L). To detect immune complexes (IC) , the IgG fraction from Fel d 1 positive sera was purified by affinity chro matography. Purified and non-absorbed material was then analysed for allerg en content and specific IgG antibody levels. immune complexes with Fel d 1 IgE were detected by coupling anti-Fel d 1 MoAb to paramagnetic particles. Results Fel d 1 was detected (0.15-1.8 mu g/L) in 23 of the 33 patients (70 %) but not from any of the controls. Eighteen samples contained IgE-Fel d 1 IC and two of four tested samples contained Fel d 1 in the IgG fraction. E lectrophoresis and Western blotting of IgG purified material using anti-Fel d 1 MoAb corroborated the presence of IgG-Fel d 1 IC. Conclusion Free-circulating inhalant allergen and IC with allergens may con tribute to maintaining immune responsiveness and sensitivity.