Heterogeneity of polyclonal IgE characterized by differential charge, affinity to protein A, and antigenicity

Abstract

Functional and physical heterogeneity of polyclonal IgE has been reported. Extremely low serum concentrations of IgE have limited the study of these important differences. We have purified polyclonal dog IgE and developed polyclonal and monoclonal (mAb C2) anti-dog IgE antibodies. In this study chromatofocusing of dog IgE revealed two biologically active IgE fractions: IgE1 eluted at pH 5.0, and IgE2 eluted at pH 4.7. The two IgE subforms (IgEs) exhibited typical IgE characteristics: positive in the 48-hour passive cutaneous anaphylaxis response, heat-labile, identical molecular weight, and reactive to polyclonal anti-dog IgE. However, the two IgEs were found to be significantly heterogeneous. IgE1 bound to protein A and did not react with mAb C2 in ELISA and isoelectric focusing-immunoblotting, whereas IgE2 did not bind to protein A and reacted with mAb C2. Further, in sodium dodecylsulfate-polyacrylamide gel electrophoresis and immunoblotting, IgE2, but not IgE1, reacted with seven well-defined mAb anti-human IgE antibodies and an mAb anti-mouse IgE antibody, even though both IgE1 and IgE2 reacted with polyclonal anti-human and anti-mouse IgE. Neuraminidase or endoglycosidase treatment did not abolish the differential antigenicity and charge of IgE1 and IgE2, although the antigenicity of IgE2 was significantly reduced after incubation with endoglycosidase. These data suggest that carbohydrate moieties are not involved in the observed differences in antigenicity and charge and that the two IgE molecules represent distinct isotypes. In studies with seven purified IgE fractions obtained from different ragweed-allergic dogs, the distribution of ragweed IgE2 varied 200-fold, whereas ragweed total IgE levels varied only fourfold. This raises the possibility of a relationship between different IgEs and the allergic response.