2.6.2. Isolation of peripheral blood mononuclear cells (PBMCs)
Isolation of peripheral blood mononuclear cells was separated from venous blood of healthy volunteers. Blood was
diluted 1:2 with phosphate-buffered saline (PBS, pH 7.2), layered on Histopaque (Sigma, Steinhem, Germany), washed
thrice with PBS and resuspended in complete RPMI-1640 supplemented with 10% fetal calf serum (FCS). The cells
were counted and resuspended at a concentration of 1×106 cells/ml in RPMI supplemented with 10% FCS. Cell
viability was determined using the tryphan blue dye exclusion test. Viability of more than 95% was satisfactory.
2.6.3. Quantification of cytokines after treatment with plant extracts
A one-ml culture of PBMC (1×106 cells) was setup in 24-well tissue culture plates (Corning, USA) and stimulated
with heat-killed P. acnes (108 organisms/ml) in the presence or absence of different crude extracts of plants at
concentrations of 5 and 50 μg/ml. Cultures were incubated at 37 °C for 18 h in a humidified atmosphere containing 5%
CO2. Cultures without stimulants were set up as controls. The following day, cultures were transferred to microfuge
tubes and centrifuged to collect cell-free supernatant containing secreted cytokines.
Cell-free supernatants were analyzed for TNF-α by commercially available sandwich ELISA (Biosource, USA).
The ratio (%) of inhibition of the cytokine release was calculated using the following equation:
Degree of inhibitionð%Þ ¼ 100 ð1−T=CÞ
T represents the concentration of cytokines in culture supernatant with the test compound.
C represents the concentration of cytokines in culture supernatant with the solvent.