Identification of main allergens from Dermatophagoides farinae and their properties under native and dissociating conditions

Dermatophagoides farinae extract has been fractionated by preparative isoelectric focusing. Fraction analysis showed that the total allergenic potency was distributed along pI values from 4.4 to 7, and most native proteins within this pI range bound specific human IgE as demonstrated by immunoblotting. Polyacrylamide gel electrophoretic analysis of the 3 active fractions, mean pI values 4.6, 5.5 and 6.8, showed that the 3 fractions basically contained the same sodium dodecyl sulfate (SDS) dissociated polypeptides, irrespective of their pIs under native conditions. However, quantitative differences were apparent, specially for a polypeptide of molecular weight (MW) 29,000 daltons and a second one of MW 18,000-20,000 daltons which were prominent in the fraction of mean pI 6.8. These two polypeptides showed to contain intrachain disulfide bonds as they moved faster in absence than in presence of beta-mercaptoethanol. After crossed radioimmunoelectrophoresis the 3 fractions displayed 3 main allergens common to all of them. The most important could be proved to contain a MW of 29,000 daltons, while the other 2 had a higher relative mobility with apparent MW of 18,000-20,000 daltons. A 4th allergen only detected at pI 4.6 could not be identified by SDS-PAGE. The MW 29,000-dalton polypeptide was sometimes seen splitted into 2 discrete bands with IgE-binding ability, but the explanation for this behavior is not yet known.