A gene/gene product interaction network of smoking correlated genes. Networks of gene/gene product interaction were generated using IPA (Ingenuity® Systems, www.ingenuity.com). Genes or gene products are represented as nodes, and the biological relationship between two nodes is represented as an edge (line). All edges are supported by at least one published reference. Solid edges represent a direct relationship and dashed edges represent an indirect relationship. Node color represents the correlation of expression level with smoking, and the color intensity indicates the degree of correlation (red represents positive correlation while green represents negative correlation). The shape of each node represents the functional class of the gene product, as shown in the key. Yellow nodes indicate exogenous toxicants manually added to the network. Genes known to be involved in immune/inflammatory response are highlighted in orange.