Fungal α-1,3-Glucan as a New Pathogen-Associated Molecular Pattern in the Insect Model Host Galleria mellonella.

Sylwia Stączek,Agnieszka Zdybicka-Barabas,Adrian Wiater,Iwona Wojda,Małgorzata Cytryńska,Paweł Mak,Krzysztof Skrzypiec,Piotr Suder

doi:10.3390/molecules26165097

Abstract

Recognition of pathogen-associated molecular patterns (PAMPs) by appropriate pattern recognition receptors (PRRs) is a key step in activating the host immune response. The role of a fungal PAMP is attributed to β-1,3-glucan. The role of α-1,3-glucan, another fungal cell wall polysaccharide, in modulating the host immune response is not clear. This work investigates the potential of α-1,3-glucan as a fungal PAMP by analyzing the humoral immune response of the greater wax moth Galleria mellonella to Aspergillus niger α-1,3-glucan. We demonstrated that 57-kDa and 61-kDa hemolymph proteins, identified as β-1,3-glucan recognition proteins, bound to A. niger α-1,3-glucan. Other hemolymph proteins, i.e., apolipophorin I, apolipophorin II, prophenoloxidase, phenoloxidase activating factor, arylphorin, and serine protease, were also identified among α-1,3-glucan-interacting proteins. In response to α-1,3-glucan, a 4.5-fold and 3-fold increase in the gene expression of antifungal peptides galiomicin and gallerimycin was demonstrated, respectively. The significant increase in the level of five defense peptides, including galiomicin, corresponded well with the highest antifungal activity in hemolymph. Our results indicate that A. niger α-1,3-glucan is recognized by the insect immune system, and immune response is triggered by this cell wall component. Thus, the role of a fungal PAMP for α-1,3-glucan can be postulated.

Highlights

The detection of pathogens by the host immune system is based on the recognition of the characteristic conservative structures of microbial cells, called pathogen-associated molecular patterns (PAMPs), by appropriate pattern recognition receptors (PRRs) [1,2]
Recognition of the PAMP structures of pathogen cells is a key step in activating immune response
Our results showed that two 57-kDa and 61-kDa proteins present in the hemolymph of naive G. mellonella larvae identified as β-1,3-glucan recognition proteins bound to A. niger α-1,3-glucan

Summary

Introduction

The detection of pathogens by the host immune system is based on the recognition of the characteristic conservative structures of microbial cells, called pathogen-associated molecular patterns (PAMPs), by appropriate pattern recognition receptors (PRRs) [1,2]. The search for host mechanisms responsible for recognizing fungal pathogens has led to increased interest in cell wall polysaccharides. These compounds are absent in animal cells and at least some of them are common to all fungal species. Alpha-1,3-glucan is another cell wall polysaccharide detected in many species of the class Ascomycetes and Basidiomycetes, including pathogenic Aspergillus, Histoplasma, Blastomyces, Cryptococcus, Pneumocystis, and Coccidioides. It accounts for about 46.5%, 34.5%, and 9% of the cell wall dry weight in Histoplasma capsulatum, Blastomyces dermatitidis, and Aspergillus niger, respectively [6,7]. While β-1,3-glucan and chitin are the main components of the inner layer of the cell walls, α-1,3-glucan is a key component of the cell wall outer layer [13,14,15,16,17,18]

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Results

Conclusion