Isolation and characterization of a new basic antigen from short ragweed pollen (Ambrosia artemisiifolia)

A new basic antigen with a molecular weight of 36.5 kDa and a pI of 8.65 was purified from short ragweed pollen using ammonium sulfate precipitation, Q-sepharose chromatography and S-sepharose chromatography. The purified protein, herein referred to as Ambrosia artemisiifolia basic antigen (AaBA), migrated as a single band in SDS-polyacrylamide gel electrophoresis and isoelectric focusing, and as a single peak on reverse phase HPLC. AaBA reacted with sera from humans allergic to ragweed pollen including pooled NIH serum. AaBA and two major acidic allergens, Amb a I (antigen E) and Amb a II (antigen K), displayed immunological cross-reactivity inasmuch as they competed significantly with each other in a competition ELISA. This suggests that at least some major epitopes in all three antigens are similar; however, other possibilities like adjacent location of different epitopes cannot be ruled out at this time. Molecular weight, amino acid composition and sequence data suggest that AaBA is very similar to Amb a II whereas it is significantly different from other basic antigens purified from ragweed pollen.