CHEMICAL AND IMMUNOLOGICAL CHARACTERIZATION OF THE EXTRACELLULAR GALACTOMANNAN OF ASPERGILLUS-FUMIGATUS

The galactomannan (GM) produced extracellularly by Aspergillus fumigat us has been purified by a double sequential hydrazine-nitrous acid tre atment of the ethanol precipitate of the culture filtrate. Nuclear mag netic resonance and gas-liquid chromatography-mass spectrometry analys is have been performed on intact GM, acid-hydrolyzed GM, and oligomers resulting from the acetolysis of the acid-hydrolyzed GM. Results show that A. fumigatus GM is composed of a linear mannan core with an alph a-(1-2)-linked mannotetraose repeating unit attached via alpha-(1-6) l inkage. Side chains composed of an average of 4 to 5 beta-(1-5)-galact ofuranose units are linked to C-6 and C-3 positions of alpha-(1-2)-lin ked mannose units of the mannan. The immunoreactivity of GM and HCl-hy drolyzed GM was studied by use of human sera from aspergillosis patien ts and an antigalactofuran monoclonal antibody. The alpha-(1-2) (1-6)- mannan core is not antigenic The immunogenic galactofuran is found amo ngst several exocellular glycoproteins. According to a direct enzyme-l inked immunosorbent assay with GM as the detector antigen, only 26% of the serum samples from aspergilloma patients (all positive by immunod iffusion assays) give optical density values superior to a cutoff esti mated as the mean +/- 3 standard deviations of values obtained with co ntrol sera.