We report here that in addition to a cytoplasmic copper-zinc-containing superoxide dismutase (SOD) and a mitochondrial manganese-containing SOD, Candida albicans expresses a third SOD gene (SOD3). The deduced amino acid sequence contains all of the motifs found in previously characterized manganese-containing SODs, except the presence of a mitochondrial transit peptide. Recombinant Sod3p expressed and purified from Escherichia coli is a homotetramer with a subunit mass of 25.4 kDa. Mass absorption spectrometry detected the presence of both iron and manganese in purified Sod3p but, as determined by metal replacement experiments, the enzyme displays activity only when bound to manganese. Overexpression of SOD3 was shown to rescue the hypersensitivity to redox cycling agents of a Saccharomyces cerevisiae mutant lacking the cytoplasmic copper-zinc-containing SOD. Northern blot analyses showed that the transcription of SOD3 is induced neither by the transition from the yeast to the mycelial form of C. albicans nor by drug-induced oxidative stress. In continuous cultures, the expression of SOD3 was strongly stimulated upon the entry and during the stationary phase, concomitantly with the repression of SOD1. We conclude that Sod3p is an atypical cytosolic manganese-containing superoxide dismutase that is involved in the protection of C. albicans against reactive oxygen species during the stationary phase.
This study has shown that the preventive program was effective in reducing the colonization of the oral mucosa and dentures by Candida and thereby improving the health of the oral mucosa.
We used an experimental model of oral candidiasis in the mouse to investigate the impact of the introduction of Candida albicans into a Candida-free system. We report that 2 strains of mice with the same major histocompatibility complex haplotype (H-2d) display different kinetics of primary oral infection after topical application of the same inoculum. The mucosal reactions in both DBA/2 and BALB/c mice involve a similar recruitment of CD4+ and CD8+ T cells and of MAC-1+ cells in mucosal tissue during the infection. A carrier state is maintained following the resolution of the infection in both strains and is associated with the persistence of intraepithelial CD4+ T cells. However, there is a time-specific recruitment of gamma delta T cells that coincides with a dramatic decrease in viable Candida in the mucosal tissue; this occurs on day 3 in BALB/c mice and on day 6 in DBA/2 mice. The denouement of an oral contact with Candida is also different in the 2 mouse strains, cell-mediated immunity being triggered in DBA/2 mice but not in BALB/c mice. The different kinetics of Candida clearance in BALB/c vs DBA/2 mice may therefore signal a differential priming of T cell subsets whose modalities do not appear to be associated with the H-2 complex.
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