Scientist - News - 17-09-2008:

B. infantis modulates adverse inflammatory response
Beintema, Nienke

A new study shows that consumption of Bifidobacterium infantis can protect the host against an over-active inflammatory response – not just within the gut, but also throughout the rest of the body. The research sheds light on the cellular mechanisms behind this modulating effect.

The role of the body’s immune system is to fight off infections with pathogens. Normally the immune response is rapid and effective. Occasionally, however, the immune response can result in inflammation that is damaging to tissues. In severe cases, such as systemic sepsis, the inflammation may even cause organ failure. The new study, which was carried out at the University College Cork (Ireland), shows that B. infantis 35624modulates this adverse inflammatory effect without compromising the effectiveness of the immune response. The study was published in the August issue of Public Library of Science (PLoS) Pathogens.
The researchers examined the effect of ingestion of B. infantis 35624, a probiotic strain of human origin, on the immune response against salmonella (Salmonella typhimurium). They administered the probiotic to mice, at least three weeks prior to salmonella infection. This experimental group showed significantly increased numbers of regulatory T (Treg) cells. These cells protect the host from pathogen-induced inflammatory responses. They do this by limiting activation of the pro-inflammatory transcription factor NF-κB.
"B. infantis does not suppress the immune response to Salmonella itself," stresses lead author Liam O’Mahony. "In fact, salmonella is cleared more rapidly from these mice. Rather, the probiotic dampens down the inflammation associated with infection. This could be very important, especially in cases of systemic infection, such as sepsis."

Entire body
While past studies showed the positive effect of B. infantis 35624 on the immune defense, the Cork study now sheds light on the cellular mechanism behind this effect. Also, O’Mahony and his colleagues were the first to show that the benefits are not restricted to the gastrointestinal tract. "We found the Treg cells that were generated by consumption of the probiotic not only within the gut but also within organs such as the spleen," explains the lead scientist.
The results also give another indication for the more general health benefits. In a separate part of their study, the researchers induced an immune response by infecting one experimental group with lipopolysaccharides (LPS) rather than with salmonella. LPS are a component of the cell wall of gram negative bacteria that are detected by the host immune system. As opposed to the oral salmonella administration, the researchers injected LPS into the body cavity. Here, too, consumption of B. infantis 35624 had a modulating effect on the infection. O’Mahony: "This demonstrates that an inflammatory stimulus outside of the gastrointestinal tract is also impacted by consumption of this bacterium."

Clinical trials have previously shown that B. infantis 35624 modulates the inflammatory response in patients with irritable bowel syndrome. Building upon the results of their study, the Cork researchers are currently looking into the effects of the probiotic on other inflammatory conditions, such as arthritis.