Fungal cell wall N-linked
glycans have been studied most extensively in Saccharomyces cerevisiae and in Candida albicans. The
glycans are located on the fungal cell surface in the form of phosphomannoprotein complexes and the amount of glycosylation is influenced both by genetics and environmental factors. The
glycans, which are comprised mostly of
mannan, are important in fungal-host interactions, as they make first contact with the immune system. Initial N-linked glycosylation events take place in the endoplasmic reticulum and are conserved throughout all eukaryotes, but yeasts are capable of additional glycosylation that may result in a
glycan comprised of more than 200
mannose units. In C. albicans, the
glycan can be delineated into an inner
mannan core, which is similar to mammalian
glycoproteins, an alpha-linked
mannan backbone with alpha-oligomannosyl side chains, and beta(1,2)-oligomannosides which are phosphodiester linked to the alpha-
mannan. Both the beta-
oligomannosides, which make up the
acid-labile part of the
phosphomannan complex, and alpha-
oligomannosides, which make up the
acid-stable part of the complex, serve as adhesins in the attachment of C. albicans yeast cells to host splenic and lymph node macrophages. The beta-
oligomannosides can induce release of tumour
necrosis factor (
TNF)-alpha, and
antibodies specific to certain beta-
oligomannosides enhance host resistance to various forms of
candidiasis. The importance of the N-linked
glycans in fungal-host interactions provides rationale for further studies, which may well lead to effective immunotherapeutic strategies for prevention and, possibly, treatment of disease.