2.7. Phagocytic Activity Assay. Phagocytic activity of blood
leukocytes was determined by using the method of Seeley
et al. [17] with some modification. One mL of leukocyte
suspension was mixed with 2mL of the Congo red-stained
Saccharomyces cerevisiae cell suspension (providing a yeast
cell : leukocyte ratio of 20 : 1). The mixtures were incubated
at room temperature for 1 h. Following incubation, 1mL of
ice-cold HBSS was added and 1mL of histopaque (1.077) was
injected into the bottom of each sample tube. The samples
were centrifuge at 850 ×g for 5min to separate leukocytes
fromyeast cells. Leukocyteswere harvested andwashed twice
in HBSS. The cells were then resuspended in 1mL trypsin-
EDTA solution (5.0 g/L trypsin and 2.0 g/L EDTA, Sigma-
Aldrich) and incubated at 37∘C overnight. The absorbance of
the samples was measured at 510nmusing trypsin-EDTA as
a blank.
Congo red-stained S. cerevisiae cells were prepared as
follows. Three mL of a 0.87% (w/v) Congo red in phosphate
buffer saline (PBS) pH 7.2 was added to yeast cell suspension
(1.5 g). After incubated at room temperature for 15min, the
mixture was thoroughly mixed with 7mL of distilled water.
The resulting mixture was autoclaved for 15 min, washed
three times in HBSS, and stored at 4∘C until use. Prior to
use, the cell concentration of was adjusted to 108 cells/mL in
HBSS.