&bgr;–1,6-linked Galactofuranose- rich peptidogalactomannan of Fusarium oxysporum is important in the activation of macrophage mechanisms and as a potential diagnostic antigen

Abstract

A peptidogalactomannan (PGM) from Fusarium oxysporum was structurally characterized by a combination of chemical and spectroscopic methods, including one and two-dimensional nuclear magnetic resonance (1D and 2D NMR). The galactomannan component consists of a main chain containing (1→6)-linked β-D-galactofuranose residues with side chains containing (1→2)-linked α-D-Glcp, (1→2)-linked -β-D-Manp (1→2) and β-D-Manp terminal nonreducing end units and differs from that of Aspergillus fumigatus and Cladosporium resinae that present a main chain containing (1→6)-linked α-D-Manp residues presenting β-D-Galf as side chains of 3-4 units that are (1→5)-interlinked. The importance of the carbohydrate moiety of the F. oxysporum PGM was demonstrated. Periodate oxidation abolished much of the PGM antigenic activity. A strong decrease in reactivity was also observed with de-O-glycosylated PGM. In addition, de-O-glycosylated PGM was not able to inhibit F. oxysporum phagocytosis, suggesting that macrophages recognize and internalize F. oxysporum via PGM. F. oxysporum PGM triggered TNF-α release by macrophages. Chemical removal of O-linked oligosaccharides from PGM led to a significant increase of TNF-α cytokine levels, suggesting that their removal could exposure another PGM motifs able to induce a higher secretion of TNF-α levels. Interestingly, F. oxysporum conidia, intact and de-O-linked PGM were not able to induce IL-10 cytokine release. The difference in patient serum reativity using a PGM from F. oxysporum characterized in the present study as compared with a PGM from C. resinae, that presents the same epitopes recognized by serum from patients with aspergillosis, could be considered a potential diagnostic antigen and should be tested with more sera.