A sure association and probable cause
“There seems to be a special connection [of R. gnavus] to lupus nephritis, which is an important, major subset of disease,” said Martin Kriegel, MD, PhD, chief or rheumatology and clinical immunology at the University of Munster (Germany). Dr. Kriegel also researches the gut microbiome in lupus and was asked to comment on the new findings from NYU.
Dr. Martin Kriegel
The “difficult question is, is the bug driving the flare [as the NYU paper proposes], or is it the lupus nephritis that leads to overgrowth?” he said, noting that it “is well known that kidney disease, whether from lupus or other causes, creates disturbances in the microbiome.”
It’s “likely the case” that the pathobiome – with R. gnavus being an important pathobiont – helps to drive flares, he said. The new research shows only an association, but studies done in mice – including prior research by Dr. Silverman – support a mechanistic link, said Dr. Kriegel, also adjunct associate professor of immunobiology and of medicine at Yale University, New Haven, Conn.
Investigators in the microbiome space are moving toward more strain-level analysis – “not only measuring what organisms are there, but culturing them and sequencing them,” Dr. Kriegel noted, and the new study does just this.
The R. gnavus strains isolated during lupus flares were distinguishable from strains found in healthy people – and from strains found by other researchers in patients with inflammatory bowel disease – by their common expression of a novel type of cell membrane–associated lipoglycan. The lipoglycans were recognized by specific serum IgG2 antibodies that were detected concurrently with R. gnavus blooms and lupus flares, Dr. Silverman and his colleagues reported.
Dr. Silverman and Dr. Kriegel both study the paradigm of a gut-barrier breach, whereby pathogenic bacteria cause intestinal permeability, allowing bacterial leakages that trigger inflammation and immune responses. “We think that in lupus and other rheumatic diseases like rheumatoid arthritis, a leaky gut barrier is an important mechanism, even though these patients don’t have gastrointestinal symptoms,” said Dr. Kriegel, who has studied the role of another potentially pathogenic bacteria, Enterococcus gallinarum, in SLE.
Strengthening the gut barrier may be a plausible, general approach to reducing the severity of diseases like SLE and RA until more personalized approaches targeting individuals’ microbiome are developed, he noted.
Future treatments involving antibacterial agents, probiotics or dietary regimens that prevent imbalances in the gut microbiome would be “benign,” compared with currently utilized immunosuppressive medications, Dr. Silverman said.
The NYU study was funded in part by grants from the National Institutes of Health and the Lupus Research Alliance. Dr. Silverman disclosed that NYU has filed a patent application for an antibody test to detect serum antibodies to the lipoglycan made by some strains of R. gnavus. Dr. Kriegel disclosed that he holds a patent at Yale related to the Enterococcus bacteria he studies, and that he consults for Roche, Enterome, and Eligo Biosciences.