Ruminococcus gnavus and the big bad lupus

The microbiota was suspected to play a role in lupus (at least in its most common form called “systemic lupus erythematosus or SLE”), a rare chronic autoimmune disease which is difficult to diagnose. Thanks to recent work by an American team, a specific bacterium has now been singled out: Ruminococcus gnavus.

 

“What about lupus?” Fans of House M.D. are familiar with the name of this uncommon disease. It gained its name due to the wolf shape that sometimes appears on the faces of people with lupus. However, lupus is not easily diagnosed because symptoms are not specific: fatigue, skin rashes, joint pain, hair loss, fever... or, in severe forms, damage to vital organs such as kidneys or heart. Which is why the team of the famous small-screen diagnostician often hesitates. But why are the symptoms so diverse? Because it is a disease related to a deregulation of the immune system which attacks the body’s own cells in different parts of the body, in flares. And the gut microbiota seems to be involved.

Microbiota crises and imbalances

Researchers were already aware that patients with lupus generally have reduced bacterial diversity in the gastrointestinal tract that is often combined with an imbalance in bacterial levels (i.e. “dysbiosis”), compared to healthy subjects. But until now, the microbiota of patients experiencing flares had rarely been characterized.  It has now been done thanks to recent work carried out on around sixty women with lupus. The results indicated that periods of microbiota imbalance coincided with lupus flares.

Is Ruminococcus gnavus to blame?

Researchers were able to identify a bacterium, Ruminococcus gnavus, whose overabundance was correlated to the disease’s activity, especially in patients with kidney inflammation (or nephritis) and took place at the expense of beneficial bacteria known for their anti-inflammatory effect. This imbalance goes hand in hand with an alteration of the intestinal barrier, which exposes even more the immune system to gut bacteria, some of which turn out to be pathogenic. In the future, these preliminary findings give us hope that someday, House will be able to easily diagnose and monitor cases of lupus thanks to the development of a biomarker related to R. gnavus.

 

Sources:

Azzouz D, Omarbekova A, Heguy A et al. Lupus nephritis is linked to disease-activity associated expansions and immunity to a gut commensal. Ann Rheum Dis 2019. PMID 30782585