Abstract
Pathogens reduce immune recognition of their cell surfaces using a variety of inert structural polysaccharides. For example, capsular polysaccharides play critical roles in microbial survival strategies. Capsules are widely distributed among bacterial species, but relatively rare in eukaryotic microorganisms, where they have evolved considerable complexity in structure and regulation and are exemplified by that of the HIV/AIDS-related fungus Cryptococcus neoformans. Endemic fungi that affect normal hosts such as Histoplasma capsulatum and Blastomyces dermatitidis have also evolved protective polysaccharide coverings in the form of immunologically inert α-(1,3)-glucan polysaccharides to protect their more immunogenic β-(1,3)-glucan-containing cell walls. In this review we provide a comparative update on bacterial and fungal capsular structures and immunogenic properties as well as the polysaccharide masking strategies of endemic fungal pathogens.
Highlights
Surface structures delineating the host-pathogen interface are critical to the outcome of microbial infections
In this review we will provide an overview of protective capsule structures and related masking mechanisms comparing the fungal pathogen, Cryptococcus neoformans with representative bacterial and fungal pathogens
Comparisons of polysaccharide capsule (PC) loci suggest a variety of genetic mechanisms and show that the core machinery involved in the synthesis and polymerization of repeat unit vary widely and are often non-homologous between serotypes
Summary
Surface structures delineating the host-pathogen interface are critical to the outcome of microbial infections. The external structures of microbes include viral envelopes, parasite surface protectants, as well as capsules and cell walls of bacteria and fungi. These protein, lipid, or carbohydrate masks range from. Polysaccharide capsules (PC) are important virulence factors in many pathogenic microbes that provide a protective coat against host immunity. They are highly diverse hydrated structures that provide microbes with a key defense against the host immune system [2]. Other fungal pathogens including the endemic fungi, Histoplasma capsulatum and Blastomyces dermatitidis which cause pulmonary disease in immunocompetent hosts, have non-capsular masking strategies that incorporate immunotolerant carbohydrates within their cell wall. In this review we will provide an overview of protective capsule structures and related masking mechanisms comparing the fungal pathogen, Cryptococcus neoformans with representative bacterial and fungal pathogens
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