Applied and Environmental Microbiology vol:81 pages:2050-2062
Recently, spaCBA-encoded pili were identified on the cell surface of L. rhamnosus GG as key molecules for binding to human intestinal mucus and Caco-2 intestinal epithelial cells. Here, we investigated the role of the SpaCBA pilus of L. rhamnosus GG in the interaction with macrophages in vitro by comparing the wild-type with surface mutants. Our results show that SpaCBA pili play a significant role in the adhesion capacity to macrophages, and also promote bacterial uptake by these phagocytic cells. Interestingly, our data suggest that SpaCBA pili also mediate anti-inflammatory effects by induction of interleukin-10 (IL-10) mRNA and reduction of interleukin-6 (IL-6) mRNA in a murine Raw 264.7 macrophage cell line. These pili appear to mediate these effects indirectly by promoting close contact with the macrophages, facilitating other surface molecules to exert anti-inflammatory effects via yet unknown mechanisms. Blockage of complement receptor 3 (CR3), previously identified as a receptor for streptococcal pili, significantly decreased the uptake of pili-expressing strains in Raw 264.7 cells, while the expression of IL-10 and IL-6 mRNA by these macrophages was not affected by this blocking. On the other hand, blocking Toll-like receptor 2 (TLR2) significantly reduced the expression of IL-6 mRNA irrespective of the presence of pili.