The ability of Candida albicans to establish an
infection involves multiple components of this fungal pathogen, but its ability to persist in host tissue may involve primarily the immunosuppressive property of a major cell wall
glycoprotein,
mannan.
Mannan and
oligosaccharide fragments of
mannan are potent inhibitors of cell-mediated immunity and appear to reproduce the immune deficit of patients with the mucocutaneous form of
candidiasis. However, neither the exact structures of these inhibitory species nor their mechanisms of action have yet been clearly defined. Different investigators have proposed that
mannan or
mannan catabolites act upon monocytes or suppressor T lymphocytes, but research from unrelated areas has provided still other possibilities for consideration. These include interference with
cytokine activities, lymphocyte-monocyte interactions, and leukocyte homing. To stimulate further research of the immunosuppressive property of C. albicans
mannan, we have reviewed (i) the relationship of
mannan to other
antigens and
virulence factors of the fungus; (ii) the chemistry of
mannan, together with methods for preparation of
mannan and
mannan fragments; and (iii) the historical evidence for immunosuppression by Candida
mannan and the mechanisms currently proposed for this property; and (iv) we have speculated upon still other mechanisms by which
mannan might influence host defense functions. It is possible that understanding the immunosuppressive effects of
mannan will provide clues to novel
therapies for
candidiasis that will enhance the efficacy of both available and future anti-Candida agents.