Properties of Probiotics as Therapeutics
It appears that the VSL3 probiotics mixture acts directly on the epithelium to enhance barrier integrity, thus demonstrating that other mechanisms of action different from the enhancement of IL-10 stimulation are likely to be involved in the antiinflammatory action of probiotics (62). The anti-inflammatory actions of probiotic bacteria on the intestinal epithelial cells occurred through inhibition of NFKB, since, as stated above, immune cells can distinguish prokaryotic DNA from vertebrate DNA by detecting methylated CpG dinucleotides.
Bacterial DNA may therefore activate both innate and acquired immune responses. It is not known yet whether DNA from different bacterial species have differential immune responses. Intestinal epithelial cells are key components in the mucosal immune system, but it is still unknown whether TLR9, which participate in bacterial DNA recognition, are expressed in the epithelial cells.
In their study they examined the effect of DNA from probiotic and pathogenic bacteria on cytokine release from epithelial cells and murine ~ splenocytes. Madsen et al. (93) used DNA from VSL3 probiotics or DNA from the pathogenic bacteria, S. typhimurium in a murine intestine model in the presence or absence of LPS. Live VSL#3 bacteria (103-107 CFU/ml) or isolated DNA (10 I-Ig/ml) was applied to confluent HT-29 cells for 1 hour, followed by S. typhimurium, TNF-a. or IL-1. NFKB activation and IL-8 release into the supernatant were measured by EMSA and ELISA, respectively.
Splenocytes were isolated from IL-10 deficient mice and stimulated with fecal bacterial sonicates in the presence and absence of VSL#3 DNA or E. coli DNA. In intestinal tissue the presence of VSL#3 DNA, but not S. typhimurium DNA resulted in a 45% and 50% reduction in basal and LPS-stimulated IFN-ysecretion respectively.
In HT-29 monolayers, VSL#3 and VSL#3 DNA resulted in a significant dose-dependent attenuation of IL-8 secretion and NFKB activation in response to S. typhimurium, TNF-a., and IL-1. In splenocytes, VSL#3 DNA, but not E. coli DNA, attenuated stimulated IFN-y secretion by 98% and IL-12 by 64%.
Thus, immune and epithelial cells may recognize and respond to DNA from probiotic bacteria with a down-regulation of proinflammatory cytokine secretion and, in intestinal epithelial cells, an attenuation of the NFKB signal pathway.