Abstract
Lactobacillus rhamnosus GG (LGG) cells have been shown to promote type-1 immune responsiveness; however knowledge of immunomodulation of soluble factors secreted by LGG is limited. This is the first study to investigate whether LGG soluble factors promote a comparable immune responsiveness as the bacterial cells. Both treatments − LGG conditioned medium with (CM + LGG) or without (CM) LGG cells, in this study increased expression of several toll-like receptors (TLRs) in all studied cell types and antigen presentation-associated receptor HLA-DR in macrophages and “intermediate” monocytes; but decreased that of activation markers on monocytes and macrophages and production of IL-10, IL-12 and TNFα in macrophages. In co-culture with mononuclear cells, CM increased Th1-type cytokine profile but not as pronounced as CM + LGG. This study suggests that LGG soluble factors exert similar immunomodulatory effects as the intact cells, but cells may be required for optimal type-1 immune responsiveness polarizing capacity of this probiotic strain.
Highlights
Conditioned medium of lactobacilli, which is cell-free supernatant containing soluble factors, has been shown to enhance lactobacilli but inhibit invasive Escherichia coli, adhere to intestinal epithelial cells, intestine mucus and gastric mucin[1,2]; and elicit antibacterial activity against pathogens such as Salmonella species[3,4,5]
This study aimed to investigate whether Lactobacillus rhamnosus GG (LGG) soluble factors promote the same immune responsiveness as the cells, and if LGG cells alter the immunomodulatory properties of the soluble factors
They were detected after 24-hour incubation with conditioned medium (CM) or CM + LGG
Summary
Conditioned medium of lactobacilli, which is cell-free supernatant containing soluble factors, has been shown to enhance lactobacilli but inhibit invasive Escherichia coli, adhere to intestinal epithelial cells, intestine mucus and gastric mucin[1,2]; and elicit antibacterial activity against pathogens such as Salmonella species[3,4,5]. Lactobacillus rhamnosus GG (LGG) (ATCC 53103) is perhaps the most researched lactobacilli in the world; but some of its soluble factors have only been recently identified, for example, p75 and p40 proteins[7], porcine serpine protease inhibitor, glyceraldehyde-3-phosphate dehydrogenase (GAPDH), cell wall-associated hydrolase, transcriptional regulator and phosphoglycerate kinase[8]. These factors play an important role in the physiology of LGG8–12 and have been found beneficial to the gut, for example, diminishing apoptosis of intestinal epithelium[7,13], enhancing intestinal crypt survival[13] and preserving cytoskeletal integrity of intestine[14]. Elucidating the immunomodulatory effects of LGG soluble factors will help to draw evidence-based guidelines of this strain for the treatment development for various diseases such as drug synthesis and vaccine development
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