Fungal Wall Components and Immunostimulation

Mannose-based molecular patterns on stealth microspheres for receptor-specific targeting of human antigen-presenting cells

The targeting of antigen-presenting cells has recently gained strong attention for both targeted vaccine delivery and immunomodulation. We prepared surface-modified stealth microspheres that display various mannose-based ligands at graded ligand densities to target phagocytic C-type lectin receptors (CLRs) on human dendritic cells (DCs) and macrophages. Decoration of microspheres with carbohydrate ligands was achieved (i) by electrostatic surface assembly of mannan onto previously formed adlayers of poly( l-lysine) (PLL) or a mix of PLL and poly( l-lysine)- graft-poly(ethylene glycol) (PLL-PEG), or (ii) through assembly of PLL-PEG equipped with small substructure mannoside ligands, such as mono- and trimannose, as terminal substitution of the PEG chains. Microspheres carrying mannoside ligands were also studied in combination with an integrin-targeting RGD peptide ligand. Because of the presence of a mannan or PEG corona, such microspheres were protected against protein adsorption and opsonization, thus allowing the formation of specific ligand-receptor interactions. Mannoside density was the major factor for the phagocytosis of mannoside-decorated microspheres, although with limited efficiency. This strengthens the recent hypothesis by other authors that the mannose receptor (MR) only acts as a phagocytic receptor when in conjunction with yet unidentified partner receptor(s). Analysis of DC surface markers for maturation revealed that neither surface-assembled mannan nor mannoside-modified surfaces on the microspheres could stimulate DC maturation. Thus, phagocytosis upon recognition by CLRs alone cannot trigger DC activation toward a T helper response. The microparticulate platform established in this work represents a promising tool for systematic investigations of specific ligand-receptor interactions upon phagocytosis, including the screening for potential ligands and ligand combinations in the context of vaccine delivery and immunomodulation.

Antioxidative and antimutagenic activity of yeast cell wall mannans in vitro

Antioxidative and antimutagenic effect of yeast cell wall mannans, in particular, extracellular glucomannan (EC-GM) and glucomannan (GM-C.u.) both from Candida utilis, mannan from Saccharomyces cerevisiae (M-S.c.) and mannan from Candida albicans (M-C.a.) was evaluated. Luminol-dependent photochemical method using trolox as a standard showed that EC-GM, GM-C.u., M-S.c. and M-C.a. have relatively good antioxidative properties. EC-GM exhibited the highest antioxidative activity, followed by GM-C.u. and M-S.c. M-C.a. showed the least antioxidative activity. These mannans were experimentally confirmed to exhibit different, statistically significant antimutagenic activity in reducing damage of chloroplast DNA of the flagellate Euglena gracilis induced by ofloxacin and acridine orange (AO). We suggest that the antimutagenic effect of EC-GM, GM-C.u., M-S.c. and M-C.a. against ofloxacin is based on their ability to scavenge reactive oxygen radicals. With AO, the reduction of the chloroplast DNA lession could be a result of the absorptive capacity of the mannans. The important characteristics of mannans isolated from the yeast cell walls, such as good water solubility, relatively small molecular weight (15-30kDa), and antimutagenic effect exerted through different mode of action, appear to be a promising features for their prospective use as a natural protective (antimutagenic) agents.

Glucomannan from Candida utilis. Structural investigation

Structure of the glucomannan isolated from the cell walls of Candida utilis has been investigated using acetolysis fragmentation, methylation analysis and NMR spectroscopy. The structure of the glucomannan resembles that of the cellular mannans of other Candida species, except that the longer tetra- and pentassacharide side-chains are terminated with a glucosyl residue. Presence of the nonreducing glucosyl groups at the ends of the side-chains caused the C. utilis not to cross-react in a double immunodiffusion test with other Candida species that possess mannan antigens and cross-react with Hansenula species with glucomannan antigens.