Modulation of cellular innate immune responses by lactobacilli

Lactobacillus is a genus of lactic acid bacteria frequently used as healthpromoting probiotics. Using probiotics to treat or prevent infections is a novel experimental approach with vast impact on future therapy. Lactobacillus rhamnosus GR-1 is a probiotic investigated for its ability to reduce urogenital disease including urinary tract infections caused by pathogenic Escherichia coli. L. rhamnosus GR-1 has been shown to modulate immunity, thought to influence its probiotic effect. In this thesis, the aim was to study immunomodulation by L. rhamnosus GR-1 and other lactobacilli, with emphasis on elicited immune responses such as nuclear factor-kappaB (NF-κB) activation and cytokine release from human urothelial cells. Viable, heat-killed, and isolated released products from L. rhamnosus GR-1 augmented NF-κB activation in E. coli-challenged urothelial cells. Blocking of lipopolysaccharide binding to toll-like receptor 4 completely quelled this augmentation. Size-fractionation, urothelial cell challenge, and two-dimensional gel electrophoresis of L. rhamnosus GR-1 released products presented several candidate proteins with NF-κB modulatory actions including chaperonin GroEL, elongation factur Tu, and a protein from the NLP/P60 protein family. While tumor necrosis factor was correspondingly augmented by L. rhamnosus GR-1, the release of two other cytokines, interleukin (IL)-6 and CXCL8, was reduced. Similar effects were observed in macrophage-like cells stimulated with L. rhamnosus GR-1. Many immunomodulatory effects of lactobacilli are believed to be species and strain dependent. Therefore, twelve Lactobacillus strains were used to screen for their effects on CXCL8 release from urothelial cells. A majority of these strains were able to influence CXCL8 release from the cells. Phylogenetic analysis revealed close evolutionary linkage between lactobacilli with similar actions on CXCL8. Increased knowledge on probiotic bacterial products and the mechanism(s) of action could lead to improved future treatments for infections