Lupus isn't pleasant. The chronic autoimmune disease, which takes several forms, can attack the tissues and organs of the body and lead to pain, swelling, extreme fatigue, rashes, and headaches.
Current treatments focus on managing the condition because there is no cure.
Progress is being made: in understanding the root causes of lupus, its common triggers, and in finding new therapies. But with 1.5 million people in the US affected by systemic lupus erythematosus (SLE), the most common form of the disease, there's a real urgency to this research.
Now, researchers have for the first time identified a gut bacterium closely connected to the onset of lupus, publishing their findings in Nature Communications.
Led by a team from the University of Texas Health Science Center at San Antonio (UT Health SA), the researchers used doses of the Faecalibacterium prausnitzii bacteria in mice models of lupus to successfully reduce multiple biomarkers of the condition.
"This is the first time in lupus research that we have identified a bacterium that is depleted, and when returned, it helps," says microbiologist Laurence Morel from UT Health SA.
The bacterium itself is far from new to scientists, and neither is its connection to lupus, but we now have a much better picture of its potentially protective effects.
F. prausnitzii is one of the most abundant 'good' types of gut bacteria around, and past studies have shown that people with untreated lupus have less of this kind of bacteria in their microbiome.
We also know from past research that F. prausnitzii boosts the gut's ability to digest fiber and helps to keep the lining between the colon and the rest of the body healthy.
"Oral supplementation of F. prausnitzii or bacterial culture supernatants has been shown to mitigate inflammatory response" in animal models of other diseases, the researchers write in their paper.
All of this evidence helped point the researchers towards F. prausnitzii, but there were still questions over how it interacted with lupus, and why it might potentially help.
"Given the pivotal role of F. prausnitzii in gut microbiome function and the defi-
ciency of the species in SLE patients, we investigated whether supplementation of F. prausnitzii restores lupus-associated microbiome dysfunction," the team explains.
They looked at the genes that were switched on in F. prausnitzii, and the chemicals being produced. They found that a loss of the bacteria, and subsequently less of the short chain fatty acid butyrate, led to damage to the mucin cells lining the gut.
When more F. prausnitzii was introduced into the mice's guts, this effectively reset the system. Fiber digestion improved again, anti-inflammatory cells became more abundant, and positive changes were seen in the kidneys and spleen, too.
This is promising because if lupus is left untreated in humans, it can lead to kidney damage that gets so bad it requires transplantation.
It's still early days – and this has only been tested in mice younger than the age when lupus symptoms develop – but it's encouraging evidence that F. prausnitzii treatments could help rebalance a natural deficit.
"If you have less bacteria digesting that fiber, you have less short chain fatty acids and a more pro-inflammatory condition," says microbiologist Yong Ge, from UT Health SA.
"We were very excited that a single probiotic strain could do such big things."
It's worth noting that F. prausnitzii isn't found in most common probiotics because of two characteristics that may complicate eventual treatments: It doesn't stick around long in the body and is inactivated by oxygen.
So, the researchers plan to examine how the chemicals produced by F. prausnitzii interact with the body's immune cells – which should tell them more about how its effects could be replicated in a medication.
Related: Lupus Patients Go Into Remission in 'Spectacular' Immunotherapy Trial
There are a huge number of influences affecting our gut microbiomes and immune systems, and many of them could be working together to trigger lupus (and could be targeted by treatments).
Because diet can so readily change our gut microbiome, the team wants to investigate this next, to see how diet impacts F. prausnitzii levels and lupus biomarkers.
"We want to put all of this together for a mechanistic, stringent study linking different carbohydrates in the diet with health outcomes," says Morel.
The research has been published in Nature Communications.
This article was fact-checked by Carly Cassella and edited by Clare Watson. While we pride ourselves on our process, we are only human. If you spot a mistake, please let us know.