Then, the cells were harvested by centrifugation, washed twice in PBS (pH 7.2), re-suspended in RPMI 1640 medium (buffered to a pH of 7.0 with 0.165 M morpholinepropanesulfonic acid), and counted after serial dilution by a hemocytometer. Human serum Human serum (HS) was see more pooled from healthy blood donors, and heat-inactivated serum was prepared by heating at 56°C for 30 min. Proteinase K-treated serum was prepared by incubating with 50 mg/mL proteinase K at 58°C for 1 h
followed by incubation at 85°C for 1 h to inactivate the protease. All fractions were filter-sterilized (0.22-mm pore size filter). Biofilm formation Fungal biofilms were prepared as described on commercially available, pre-sterilized, flat-bottomed 96-well PD-1 phosphorylation polystyrene microtiter plates (Corning) [39]. Briefly, a cell suspension of 1.0 × 106 cells/ml was prepared in RPMI 1640 and RPMI
1640 + 50%, 10%, 5% or 3% HS. From those suspensions, 100 μl was introduced into wells and incubated at 37°C for 24 h without agitation, which allowed the cells to attach to the surface of the plate and form the biofilm structure. To investigate the effect of HS on pre-adhered biofilms, C. albicans biofilms were prepared for 90 min (the adhesion phase) at 37°C as described above. The wells were washed twice with PBS to remove loosely adherent cells. Then, fresh RPMI 1640 (100 μl), containing different concentrations (3–50%) of HS were added and the plate was further incubated for 24 h at 37°C. RPMI 1640 medium without HS was included in control wells. The metabolic activity of the C. albicans this website biofilms was determined quantitatively using XTT reduction assay. Dynamic monitoring of the adhesion process Standard cell suspension of C. albicans was prepared in RPMI1640 or RPMI1640 containing different concentrations C-X-C chemokine receptor type 7 (CXCR-7) (3% to 50%) of HS, and 100 μl of those suspensions was introduced into 96-well polystyrene microtiter plates. After standing for 3 min, the plates were placed on Live Cell Movie Analyzer (JuLI™ Br., NanoEnTek Inc., Seoul, Korea) and incubated at 37°C. The instrument was set to continuous photographing mode with exposure 5%, brightness 13%, zoom level 4, interval 1 min, and total time 2 h (the experimental
group was prolonged to 3 h). When it was finished, a total of 121 or 181 photos were obtained for the control and experimental groups, respectively. Then, those pictures were played back in rapid succession to observe the dynamic changes of the fungal cells (playing at a speed of 10 frames/s). Quantitation of biofilms At the end of the incubation, the supernatant was aspirated and the wells washed twice with PBS. The quantitation of biofilms was determined using 2,3-bis (2-methoxy-4-nitro-5-sulfo-phenyl)-2H-tetrazolium-5-carboxanilide (XTT) reduction assay that measures the activity of mitochondrial dehydrogenase [40]. XTT solution (1 mg/ml) was prepared by dissolving XTT powder (Sigma, Shanghai, China) in PBS, and the solution was filter-sterilized (0.22-mm pore size filter).