Lactobacilli and streptococci induce inflammatory chemokine production in human macrophages that stimulates Th1 cell chemotaxis

Macrophages have a central role in innate-immune responses to bacteria. In the present work, we show that infection of human macrophages with Gram-positive pathogenic Streptococcus pyogenes or nonpathogenic Lactobacillus rhamnosus GG enhances mRNA expression of inflammatory chemokine ligands CCL2/monocyte chemoattractant protein-1 (MCP-1), CCL3/macrophage-inflammatory protein-1alpha (MIP-1alpha), CCL5/regulated on activation, normal T expressed and secreted, CCL7/MCP-3, CCL19/MIP-3beta, and CCL20/MIP-3alpha and CXC chemokine ligands CXCL8/interleukin (IL)-8, CXCL9/monokine induced by interferon-gamma (IFN-gamma), and CXCL10/IFN-inducible protein 10. Bacteria-induced CCL2, CCL7, CXCL9, and CXCL10 mRNA expression was partially dependent on ongoing protein synthesis. The expression of these chemokines and of CCL19 was dependent on bacteria-induced IFN-alpha/beta production. CCL19 and CCL20 mRNA expression was up-regulated by IL-1beta or tumor necrosis factor alpha (TNF-alpha), and in addition, IFN-alpha together with TNF-alpha further enhanced CCL19 gene expression. Synergy between IFN-alpha and TNF-alpha was also seen for CXCL9 and CXCL10 mRNA expression. Bacteria-stimulated macrophage supernatants induced the migration of T helper cell type I (Th1) cells, suggesting that in human macrophages, these bacteria can stimulate efficient inflammatory chemokine gene expression including those that recruit Th1 cells to the site of inflammation. Furthermore, L. rhamnosus-induced Th1 chemokine production could in part explain the proposed antiallergenic properties of this bacterium.