Characterization of a second major antigen Ag 13 (antigen C) of Aspergillus fumigatus and investigation of its immunological reactivity.

A second major antigen of Aspergillus fumigatus (Ag 13) has been identified and characterized as a 70 kD, heat-labile component which is able to bind to the lectin, concanavalin A. Ag 13 proved to be identical to the previously recognized C antigen, known to possess chymotryptic activity. A monospecific antiserum to Ag 13 has been affinity purified and used to develop a sandwich ELISA for measuring levels of Ag 13 specific IgG antibodies in patients' sera. Although all ABPA sera (25/25) had significantly raised levels, some aspergilloma sera (2/5) had only very low levels; of the control sera, 10/10 fungal atopics were negative, but 5/12 farmer's lung sera had low but positive values of Ag 13 specific IgG, i.e. sensitivity 100%, specificity 80%. Ag 13 is therefore a diagnostically important component of A. fumigatus and the antigen-specific ELISA may be of importance for the improved detection of disease-specific antibodies.