Could a bacterial polysaccharide suppress fatal brain inflammation?

Written by Alice Bough (Future Science Group)

Scientists from the City of Hope National Medical Center (CA, USA) have identified that polysaccharide A (PSA), a component of the cell envelope of Bacteroides fragilis, has the potential to prevent viral brain inflammation caused by herpesvirus.

Herpes simplex encephalitis (HSE) is an often-fatal disease and survivors frequently have severe neurological damage.

The paper, published in Nature Communications, analyzed the effect of B. fragilis PSA on the survival rate of mice infected with herpes simplex virus.

Mice that had been pretreated with the probiotic B. fragilis survived the herpes simplex virus infection while mice treated with placebo did not. Although both groups were treated with acyclovir, the standard clinical antiviral agent for HSE, this did not seem to affect the survival rates.

Further experiments in immune-deficient mice allowed the scientists to determine that the PSA interacted with B cells. This interaction then activated regulatory T cells that could reduce inflammation.

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“This mouse study shows that B. fragilis PSA can temper the immune system so that infection does not result in an uncontrolled, potentially fatal inflammatory response in the brain,” explained Edouard Cantin (City of Hope).

“Although HSE is a rare brain inflammation disorder, the lessons we learned here might, with more research, be applicable to other viral infections such as other herpesviruses, influenza virus, West Nile virus and maybe even viral respiratory diseases – conditions where inflammation begins to jeopardize the health of your body and brain function,” continued Cantin.

The results of the study highlight that symbiotic bacteria can optimize the immunity of the host. “It’s possible that consumption of certain prebiotics, probiotics or synbiotics may enhance your body’s natural ability to suppress inflammatory diseases,” commented Chandran Ramakrishna (City of Hope).

“It also seems reasonable that what you decide to eat may affect your overall health and ability to fight off disease,” concluded Ramakrishna. In addition to nutritional approaches, the authors of the study also suggested that combination treatments of bacterial symbiosis factors such as PSA and antiviral agents could be the future of treating viral inflammatory diseases.

Sources: Ramakrishna C, Kujawski M, Chu H, Li L, Mazmanian SK, Cantin EM. Bacteroides fragilis polysaccharide A induces IL-10 secreting B and T cells that prevent viral encephalitis. Nat. Comm. 10, 2153 (2019);