How do probiotics work?

It has been known for more than 30 years that Lactobacilli probiotics benefit human health (1). Why they do so remains an unanswered question. In a study(2), published this week in mBio Chunxu Gao and colleagues describe how histamine generated by the probiotic L. reuteri helps control gut immunity.

Lactobacillus reuteri is a natural part of the gut microbiome of humans, as well as other animals. It has been studied since the 1960s and is known to be prevalent in healthy individuals. L. reuteri has been widely marketed as a commercial probiotic species for more than 25 years.

Using a mouse model of Crohn’s disease, the researchers found that the L. reuteri turned the essential amino acid L-histidine (essential because we need to obtain it from food), into histamine. This bacterially-created histamine could then lower pro-inflammatory signals in the gut.

Histamine is usually associated with activating the immune system – think about the antihistamines you use to lessen an allergic reaction. However, the histamine type 2 receptor, that is found in the gut, is very different from the histamine type 1 receptor, which is the target of antihistamines. The type 2 receptor which lines the intestine conveys an immune suppression signal, thus histamine, delivered in the right place, leads to less inflammation.

The research team hopes that prescribing specific probiotic strains to patients, with the corresponding dietary supplement may be a new tactic for preventing or treating diseases in the not-so-distant future.



1.     Reid, G., et al. (1990) Is there a role for Lactobacilli in Prevention of Urogenital and Intestinal Infections? Clin. Microbiol. Rev. Oct. vol. 3 no. 4 335-344

2.     Gao, C., et al. (2015) Histamine H2 Receptor-Mediated Suppression of Intestinal Inflammation by Probiotic Lactobacillus reuteri. mBio Dec.