Immunological and physicochemical properties of a highly purified allergen from Dirofilaria immitis

Allergen in crude extract of Dirofilaria immitis was purified and separated from IgG-inducing antigens by a combination of DEAE-Sephadex A-50 chromatography, Sephadex G-200 gel filtration and starch gel zone electrophoresis. The purified preparation was proved to be one protein band by sodium dodecyl sulfate polyacrylamide gel (SDS-gel) electrophoresis and one precipitin arc by immunodiffusion. The molecular weight of the purified allergen was estimated to be approximately 20,000 by gel filtration and 15,000 by SDS-gel electrophoresis. The carbohydrate content of the preparation was apparently low, about 2%. The allergen was positively charged, and its determinant group was protein in nature. It was resistant to tryptic, pepsic and chymotryptic digestion, periodate oxidation and DNase and RNase digestion but very sensitive to pronase digestion. Allergen was inclined to aggregate each other in the buffered solution. It was also very resistant to vibration, heat (80 degrees C for 1 h) and acid (pH 2.5) and alkali (pH 11.0) treatments. Rats as well as mice immunized with allergen developed only a reaginic antibody and no hemagglutination antibody.