Principal component analysis of microarray data to demonstrate similarity of response of the cell types and treatment times. In the plot, each point represents a cell line (NHEK, Leuk1, Leuk2, or 101A) and treatment time (0 h, black circles; 24 h, gray triangles) of CSC exposure (25 μg/ml). The X, Y and Z-axes are PC#1, PC#2 and PC#3, respectively.