Vaccines and gut microbes join forces to fight flu

Gut bacteria help vaccines build stronger immunity against influenza in mice, scientists report in the Sept. 18 Immunity.

The partnership may explain why vaccines provide less protection for people living in certain places, such as rural parts of developing countries, says lead author Bali Pulendran, an immunologist at Emory University. The composition of gut microbes in people from those locations differs from the mix found in individuals from urban, developed areas, he says.

In 2011, Pulendran’s laboratory made a puzzling discovery involving seasonal influenza vaccination in humans: The vaccine instructed blood cells to produce a protein called TLR5 that normally protects the body from bacteria, not viruses.

The new study argues that bacteria influence vaccine-based immunity, at least in mice. The team found that rodents engineered to lack TLR5 protein make fewer flu-fighting antibodies after immunization than normal mice.

Mice reared to lack microbes, or rodents given antibiotics, also had a muffled antibody response after receiving the flu vaccine. The team found the same pattern with a vaccine for polio.

TLR5 protein recognizes bacteria with propulsive tails made from the protein flagellin. Only bacteria with flagellin fortify mouse immunity to flu after vaccination, the researchers found.

Gut microbes could affect vaccine potency in people, Pulendran says, though only further human studies could prove that.