We have previously demonstrated that IL-27 is a novel anti-HIV cytokine, which inhibits HIV replication in CD4 T cells and macrophages as interferon (IFN)-α does. To further understand the mechanism of the antiviral effect, we performed Affymetrix DNA microarray and gene functional annotation analysis using DAVID (the Database for Annotation, Visualization, and Integrated Discovery). DAVID is a web-based bioinformatics application that systematically identifies enriched biology associated with large gene list(s) derived from high-throughput genomic experiments, such as microarray. The enriched annotation terms identified by DAVID will give important insights into understanding the biological themes under study. Having used the DAVID bioinformatics tools, we have shown that IL-27 differentially regulates the gene expression between T cells and macrophages. IL-27 significantly induces IFN-inducible genes including antiviral genes in macrophages as does IFN-α, suggesting that IL-27 inhibits HIV replication in macrophages via a mechanism similar to that of IFN-α.