Surface antigens of intact Aspergillus fumigatus mycelium: their localization using radiolabelled protein A as marker.

Abstract

Isotopically-labelled Protein A from Staphylococcus aureus was used as a marker to quantify binding of IgG molecules to surface antigens of Aspergillus fumigatus mycelium. The IgG class antibodies were obtained from rabbits inoculated with mycelial fractions and from patients suffering from aspergillosis and aspergillus-related diseases. The highest incorporation of label was obtained with an antiserum from rabbits inoculated with A. fumigatus wall material. Antibodies raised to other antigenic fractions of A. fumigatus and antibodies from patients infected with aspergillus gave lower levels of incorporation of Protein A. In competitive binding experiments, pre-incubation of antibodies with partially purified aspergillus antigens depressed subsequent binding to the mycelial surface by 20-30% of that of the control values. Low molecular weight disaccharides and oligosaccharides were without effect in this system. Preincubation of A. fumigatus with lectins having specificities for defined sugar residues did not reduce subsequent antigen/antibody interaction. Treatment of the mycelial surface with certain proteolytic or polysaccharolytic enzymes led to a decrease in antibody binding, while pretreatment of A. fumigatus with the hydrolytic enzyme mixture of Trichoderma harzianum culture filtrate gave increased antibody binding. Aspergillus species showed different susceptibilities to enzyme action and their surface structures could be differentiated from A. fumigatus on this basis. These differences were not obvious in direct binding experiments where antibodies raised to A. fumigatus wall bound with equal facility to antigenic sites located on the walls of other Aspergillus species.