Further characterization of IgE-binding antigens from guinea pig hair as new members of the lipocalin family

Background: Guinea pigs are important sources of inhalant allergens in home and working environments. However, little is known about the molecular characteristics and the relevant epitopes of guinea pig allergens. Recently, several allergens have been identified in hair extract and urine, and the major allergen Cav p 1 (20 kDa) has been characterized. Objective: The aim of the present study was to isolate and to characterize a further major allergen from guinea pig hair with 17 kDa. Methods: Guinea pig hair extract was fractionated using anion exchange chromatography and reverse-phase high performance liquid chromatography. Analyses were carried out by sodium dodecyl sulphate–polyacrylamide gel electrophoresis, 2D-PAGE, immunoblotting, immunoblot inhibition, glycoprotein detection, and N-terminal amino acid sequencing. Results: The nonglycosylated 17 kDa allergen, which was named Cav p 2, was purified to homogeneity. On the basis its 15 N-terminal residues, there was 69% identity with a sequence of Bos d 2, an allergenic protein from cow dander belonging to the lipocalin family. The 2D-immunoblotting analyses of guinea pig hair extract demonstrated that Cav p 2 and Cav p 1, contained several isoforms with pI values ranging from 3.6 to 5.3. The 2D-immunoblot inhibition disclosed cross-reactive IgE epitopes on the allergens Cav p 2 and Cav p 1. Furthermore, Cav p 1 can form both monomers (20 kDa) and dimers (40–42 kDa). Conclusion: These studies provide important information on the isoallergen character of two relevant guinea pig allergens Cav p 1 and Cav p 2 as well as on their cross-reactive properties.