Functional Analysis of Lactobacillus rhamnosus GG Pili in Relation to Adhesion and Immunomodulatory Interactions with Intestinal Epithelial Cells

Abstract

ABSTRACTLactobacillus rhamnosusGG, a probiotic with good survival capacity in the human gut, has well-documented adhesion properties and health effects. Recently,spaCBA-encoded pili that bind to human intestinal mucus were identified on its cell surface. Here, we report on the phenotypic analysis of aspaCBApilus knockout mutant in comparison with the wild type and other adhesin mutants. The SpaCBA pilus ofL. rhamnosusGG showed to be key for efficient adherence to the Caco-2 intestinal epithelial cell (IEC) line and biofilm formation. Moreover, thespaCBAmutant induces an elevated level of interleukin-8 (IL-8) mRNA in Caco-2 cells compared to the wild type, possibly involving an interaction of lipoteichoic acid with Toll-like receptor 2. In contrast, anL. rhamnosusGG mutant without exopolysaccharides but with an increased exposure of pili leads to the reduced expression of IL-8. Using Transwells to partition bacteria from Caco-2 cells, IL-8 induction is blocked completely regardless of whether wild-type or mutantL. rhamnosusGG cells are used. Taken together, our data suggest thatL. rhamnosusGG SpaCBA pili, while promoting strong adhesive interactions with IECs, have a functional role in balancing IL-8 mRNA expression induced by surface molecules such as lipoteichoic acid.