Background: Previous characterization studies of Pityrosporum orbiculare allergens have led to contradictory results. In immunoblotting studies a range of IgE-binding proteins of 10-100 kDa have been identified. In another study, however, the IgE-binding structures were claimed to be associated with high-molecular-weight polysaccharides or glycoproteins, presumably mannans or mannoproteins.
Objective: In the present study the reasons for these discrepancies were investigated.
Methods: P. orbiculare preparations were compared in IgE ELISA and IgE-inhibition ELISA, as well as in immunoblotting with sera from atopic dermatitis patients.
Results: It was inferred that variations in the period of in vitro culture of P. orbiculare constituted the most important factor determining the different compositions of the resulting yeast cell extracts. After 2 days of culture a wide range of allergenic proteins was present but upon more prolonged culture (> 4 days) most proteins of 10-100 kDa were lost. Accordingly, the protein concentration of the extracts gradually declined from 40% to 25% between days 4 and 15 of culture. On the other hand, the carbohydrate content remained fairly constant (approximately 30%). Using inhibition ELISA it was demonstrated that the high-molecular-weight glycoproteins or polysaccharides presumably involved in most of the IgE-binding capacity in extracts from old cultures, were also present in comparable concentrations in all extracts tested, even after culture for only 2 or 4 days.
Conclusion: Preparations obtained from the exponential phase of yeast cultures (2-4 days old), should preferably be used in studies of the IgE response to P. orbiculare.