Streptococcus salivarius regulates epithelial cell gene expression and immune responses

Experimental evidence indicates resident microbial populations help maintain host-microbe homeostasis in the gut but their roles at other sites are less well studied. Streptococcus salivarius, a commensal of oral and nasopharyngeal mucosa, is reported to protect against pathogens, suggesting immunomodulatory properties. Objectives: To determine the influence of S. salivarius on (i) gene responses of epithelial cells; (ii) immune responses to other bacteria/immunomodulatory molecules. Methods: S. salivarius K12 (from Throat Guard lozenges, BLIS Technologies) were inoculated (50:1) onto the apical surfaces of polarised human bronchial epithelial cells (HBE) and RNA extracted after 1h. cDNA was hybridised to a 21K human oligo-based array (Jack Bell Research Centre). Images were quantified using Imagene software and data analysed using Arraypipe, Cytoscape, Gene Ontology Tree Machine and TIGR MeV. Expression of selected genes was confirmed by quantitative PCR. IL-8 secretion from polarised and non-polarised HBE was determined by ELISA following co-incubation with LL-37, Pseudomonas aeruginosa, lipopolysaccharide (LPS) or flagellin, each ± S. salivarius. Results: 678 genes were regulated by S. salivarius (fold-change >±1.5; p<0.06). These included genes involved in: general epithelial cell function and homeostasis; cytoskeletal remediation, cell development and migration; membrane activities; immune responses and intracellular signalling. Five were involved in innate immune pathways (TLR3, TLR4, P38, JNK, IFN). A number of regulated genes were involved in protein kinase signalling. S. salivarius reduced IL-8 secretion by HBE (p<0.01), and inhibited HBE IL-8 responses to 25 and 40µg/ml LL-37 (p<0.01), P. aeruginosa (p<0.02), and ≤5µg/ml flagellin (p<0.05). Conclusion: These results support a role for the commensal S. salivarius in maintaining host-microbe homeostasis through regulating epithelial cell gene expression and function, and down-regulating immune responses to pathogens and immunomodulatory molecules. Financial support from the Cystic Fibrosis Foundation, Genome Canada and the Society for General Microbiology is gratefully acknowledged