Galactoxylomannan does not exhibit cross-reactivity in the platelia Aspergillus enzyme immunoassay

Abstract

Given the recent report of a false-positive result in the Platelia Aspergillus enzyme immunoassay in a patient with cryptococcosis and in yeast extracts and purified galactoxylomannan of Cryptococcus neoformans, we evaluated culture extracts, purified polysaccharides, clinical specimens, and specimens from animals following experimental infection. Our results revealed no cross-reactions.

FIG. 1.

Comparison of the structures of the major repeating units of GalM from Aspergillus spp. (13) and GalXM and GXM from C. neoformans (2). The lack of antigenic cross-reactivity between GalM and GalXM in the EIA is apparent in the comparison of these structures. In comparison to the β(1→5)-galactofuranose side chain epitope linked to an α(1→2)-mannotetraose core by an α(1→6) bond in GalM, GalXM differs by the absence of β(1→5)-galactofuranose side chains and the presence instead of β(1→3)-xylomannan side chains and an α(1→6)-galactopyranose core. The lack of structural similarity between the GalM and GXM further reflects the lack of cross-reactivity of the two antigens in the anti-GalM EIA. Green, galactofuranose or galactopyranose; blue, mannopyranose; red, xylose; gray, glucuronic acid. The asterisk near the 1→3 galactofuranosylmannopyranose bond indicates that there is currently uncertainty as to whether this linakge is α or β in configuration.