Background Candida albicans （C. albicans） strains can spontaneously switch at a very low frequency from white to opaque phase. The ability to switch reversibly between white and opaque phenotype and contributes to the pathogenicity of C. albicans. White and opaque switching can be induced by various environmental signals. Previous study showed that opaque cells switch en masse to white when transferred in vitro to 37℃, the temperature of their animal host. The objective of the present study was to determine the effect of different concentration of carbon dioxide and temperature on white-opaque switching, and to determine the different anti-candida killing activity of white and opaque form by human monocyte-macrophage cell line THP-1.Methods White-opaque switching and opaque-white switching were assayed. Modified Lee＇s medium supplemented with phloxine B was used to detect white and opaque forms of C. albicans under 0.03% CO2 at 25℃, 0.03% CO2 at 37℃ and 5% CO2 at 37℃. Growth curve of C. albicans was monitored using OD value at 630 nm simultaneously. White and opaque forms of C. albicans and THP-1 cells were cocultured at ratio of 1：10. Colony serial dilutions were used to assay for intracellular candidacidal activity. MTT assay was used to measure the extracellular candidacidal activity.Results Phenotype switching was successfully induced in vitro in all three strains of C. albicans. When evaluating white to opaque switching, opaque colony proportion of all colonies was 0.572±0.087, 0.920±0.030 and 0.985±0.026 exposure of white cells to 0.03% CO2 at 25℃, 0.03% CO2 at 37℃ and 5% CO2 at 37℃. When evaluating opaque to white switching, opaque colony proportion of all colonies was 0.600±0.114, 0.983±0.003 and 0.998±0.003 exposure of white cells to 0.03% CO2 at 25℃, 0.03% CO2 at 37℃ and 5% CO2 at 37℃. No significant difference of white or opaque form growth rate was found among three conditions （P〉0.05）. THP-1 mediated extracellular anti-candida activity in white form was （79.8
LIU Ze-hu LI Min LU Xue-lian SHE Xiao-dong HU Su-quan CHEN Wei LIU Wei-da
Background β-glucan is the major structure component of Candida albicans （C. albicans） cell wall. It has been demonstrated that Dectin-1 as the principal C-type lectin pattern-recognition receptor （PRR） can recognize fungal β-glucan and induce immune responses. In this study, we sought to clarify whether insoluble β-glucan from the cell wall of C. albicans （CalG） could induce immune responses in human THP-1 monocytes （a human acute monocytic leukemia cell line） and to determine the underlying mechanisms. Methods Human THP-1 monocytes were challenged with CalG in vitro. The mRNA expression of Dectin-1, Toll-like receptors （TLR2）, proinflammatory cytokine （TNF-a） and chemokine （IL-8） was assayed by real-time reverse transcription polymerase chain reaction （RT-PCR）. The secretion of TNF-a and IL-8 were measured by enzyme-linked immunosorbent assay （ELISA）. H2O2 release was determined by microplate fluorescent assay. Western blotting was used to analyze IKB-a phosphorylation and degradation. Results Exposure of THP-1 monocytes to CalG led to increased gene expression and secretion of TNF-a and IL-8. CalG induced H2O2 release in a time-dependent manner. CalG hydrolyzed with zymolyase failed to induce gene expression and secretion of TNF-a, IL-8 and H2O2 release. CalG up-regulated the mRNA of Dectin-1, whereas the mRNA level of TLR2 was not altered. THP-1 monocytes challenged with CalG resulted in the activation of NF-KB in a time-dependent manner. Dectin-1 inhibitor laminarin blocked the CalG-induced production of TNF-a and H2O2 in THP-1 monocytes, but no such effect was observed in pretreatment with anti-TLR2 neutralizing antibody and the LPS inhibitor （polymyxin B）. Conclusion CalG may play a role in activation of immune responses in human THP-1 cells throuah Dectin-1, not TLR2.
