Patients with primary Sjogren’s syndrome (pSS) and systemic lupus erythematosus (SLE) share their gut microbial composition, which is different from the general population. Oral microbial composition, however, in different in both patient groups.
The research, “Shared gut, but distinct oral microbiota composition in primary Sjögren’s syndrome and systemic lupus erythematosus,” was published in the Journal of Autoimmunity.
Overlap of clinical symptoms is frequent in pSS and SLE. These two chronic autoimmune diseases share specific spots in chromosomes that cause disease susceptibility. Environmental factors are also shared, but little is known about their effects.
The microbial composition, or microbiota, in the gut and oral cavity may be important in the development of pSS and SLE, as recent studies showed differences compared to healthy controls. However, researchers still do not know whether the gut and oral microbiota of pSS and SLE patients are unique.
Aiming to address this gap, a team from the University of Groningen, in The Netherlands, intended to find disease-specific differences in gut and oral microbiota in patients with either disease and to determine whether the gut microbiota presents overlapping characteristics in pSS and SLE.
The investigators conducted an analysis called 16S ribosomal RNA sequencing — a common method of identifying and comparing bacteria — on fecal, buccal (cheek) swab and oral washing samples from patients with pSS or SLE, all living in the three northern provinces of the Netherlands. Fecal samples from 965 general population controls (45 years, 42% men) living in the same geographical area were also processed.
The team also analyzed possible links between individual bacteria and disease manifestations, accounting for age, sex, body mass index (BMI) and use of proton-pump inhibitors (PPIs) as possible confounding factors.
All patients were required not to take systemic antibiotics from two months before stool and oral sampling. SLE disease activity index (SLEDAI) was 4 or less to include participants with stable disease and low disease activity only.
Only three pSS patients used immunosuppressive treatments during the study. Non-steroidal anti-inflammatory drugs (NSAIDs) were used by 49% of patients with pSS. SLE patients were mainly treated with antimalarials (83%). PPIs were more common in SLE (60%) than in pSS patients (33%) and in population controls (7%).
The gut microbiota composition from 39 patients with pSS (mean age 55 years, 8% men) and 30 with SLE (47 years, 7% men) did not significantly differ. However, compared to population controls, patients with pSS or SLE showed lower bacterial richness — the number of different species — lower Firmicutes/Bacteroidetes ratio, and higher relative abundance of Bacteroides species — particularly B. vulgatus, B. uniformis and B. ovatus.
Factors significantly influencing gut microbiota composition were disease phenotype (having pSS or SLE), age, sex, BMI, smoking, PPI use, and NSAID use.
As for oral microbiota, analyses from 33 pSS and 34 SLE buccal swab samples, and from 34 pSS and 34 SLE oral washings, showed that patients with SLE had significantly higher bacterial richness and diversity than those with pSS.
Factors explaining the variation in oral microbiota included disease phenotype, number of teeth, gum disease, dry mouth scores, and severity of oral dryness sensation.
According to the investigators, these results mean that the different oral microbiota “could partially be explained by oral dryness in pSS patients.”
The team then observed that the relative abundance of Actinomyces and Lactobacillus bacteria in oral samples correlated with their relative abundance in fecal samples, and that SLE patients had higher relative abundance of Actinomyces in both oral and fecal samples and of Lactobacillus in oral samples only than pSS patients.
“This indicates that the oral microbiota composition influences that of the gut,” the team stated.
Overall, the study showed that “pSS and SLE patients share similar alterations in gut microbiota composition, distinguishing patients from individuals in the general population, while oral microbiota composition shows disease-specific differences between pSS and SLE patients,” the scientists concluded.