Studies on galactofuranose-containing glycostructures of the pathogenic mold Aspergillus fumigatus

Abstract

Galactofuranose is a hexose that is exclusively found in microbes and in particular in certain pathogenic species. In the mold Aspergillus fumigatus, it is the characteristic constituent of the cell wall component galactomannan. Detection of this carbohydrate is currently a widespread method used for diagnosis of systemic A. fumigatus infections. In this study, we raised and characterized 2 monoclonal antibodies that specifically react with galactofuranose-containing glycostructures. We investigated the distribution of surface-accessible galactomannan on different A. fumigatus morphotypes. We provide evidence that the antibodies recognize distinct antigens and are suitable to detect A. fumigatus hyphae in immunohistology. A mutant that is impaired in synthesis of galactofuranose stimulated a normal cytokine response in murine macrophages, which argues against galactomannan being a relevant PAMP, at least in mice. Purified galactomannan-specific monoclonal IgM L10-1 failed to inhibit the hyphal growth under in vitro conditions, but L10-1 binding to hyphae led to an enhanced deposition of the complement protein C1q. However, administration of purified L10-1 antibodies prior to infection was not able to protect mice. In conclusion, we have found no evidence for galactomannan being a relevant A. fumigatus PAMP and describe 2 novel galactomannan antibodies that might be valuable tools for the diagnosis of A. fumigatus infections and further analysis of the biological significance of galactomannan.