IL-18 modifies gene expression in EBV-infected BL cells. Differential gene expression in IL-18-treated versus BSA-treated BL2-B95-8 cells was analyzed using DNA microarrays. (A) Correlation analysis was performed by plotting differential gene expression (log ratio) from experiment IL-18(1) against that of experiment IL-18(2) (see “Results”). Negative values represent down-regulated genes, and positive values represent up-regulated genes. Histograms represent the frequency of genes with differential expression (log ratio). Correlation coefficient between experiments (r = 0.967) and statistical significance (P < .0001) was determined. (B) Hierarchical clustering analysis of genes differentially regulated between IL-18- and BSA-treated cells. Values a to d (see “Results”) are plotted for genes having a significant (P < .05) difference of expression. (C) Genes having a significant (P < .05) difference of expression between BSA- and IL-18-treated cells were grouped in functional categories according to the Gene Ontology Database (GO; http://www.godatabase.org). Bars represent the number of IL-18-regulated genes in the indicated functional clusters and subcategories.