Purification of a murine IgE-inducing antigen extracted from the house dust mite, Dermatophagoides pteronyssinus

A major antigen inducing IgE in mice (DpI) was purified from a crude extract of Dermatophagoides pteronyssinus (D.p.) using Sephacryl S-200 gel filtration, DE52 ion exchange chromatography and isoelectric focusing. This antigen is not one of the major D.p. human allergens. Isoelectric focusing showed a single peak of PCA activity at pI 4.7. Activity followed a broader banding pattern on polyacrylamide gel electrophoresis (PAGE). The molecular weight of DpI estimated from Sephadex G-150 chromatography was 1.7 X 10(5) daltons. Molecular weight calculated from SDS-gels (reducing), however, was 3.7 X 10(4), which may indicate a molecule with a subunit composition. DpI contained no detectable hexose as measured by the phenol-sulfuric acid assay. PCA activity of DpI was stable at 98 degrees C and to treatment with 0.1 M sodium metaperiodate, but destroyed by pronase. DpI represents approximately one per cent of the total protein of crude extracts. Purified DpI displays a specific activity increase of 40 times that of the crude extract with the PCA test. DpI is capable of inhibiting 40% of the binding between crude extract and human IgE, but only at extremely high concentrations. Human IgE was 700 times more sensitive to D.p. crude extract than purified DpI by enzyme immunoassay.