At present, the research on the pathogenesis and treatment of SLE is a difficult point in the medical field. A growing number of studies have demonstrated that human gut microbiota is one of the important factors affecting the development of autoimmune diseases [37]. In patients with SLE, the increase of some gut microbiota can inhibit the production of IL-12p70 and enhance the response of IL-8, IL-6, IL-10 and TNF-α, such as Streptococcus and Veillonella. They lead to pro-inflammatory response [35–38]. In addition, abnormally enriched, antigen mimicry and metabolic response of gut microbiota can cause the disorder of immune response [19, 39]. Thus, we tried to include as many studies as possible to obtain and extracted experiment results of alpha diversity and some gut microbiota abundance between SLE patients and healthy people, analyzing the changes of gut microbiota in SLE patients by meta-analysis. Our meta-analysis contained eleven case-control studies, comprising three hundred and seventy three SLE patients and one thousand two hundred and eighty eight healthy people, involving five countries and nine different cities.
Meta-analysis results
Our meta-analysis showed that both Shannon wiener diversity index and Chao1 richness estimator, which are used to measure diversity in specific areas or ecosystems of the intestine, decreased in patients with SLE. Chao1 richness estimator is an indicator of species richness [40]. Shannon-wiener diversity index is an index to measure the uniformity of intestinal microorganisms [41]. This means the abundance and uniformity of the gut microbiota of patients with SLE are impaired. As a result, the stability of the micro-community is reduced, the structure and function of the micro-community are weakened, and the ability to resist changes is reduced.
Compared with healthy people, the relative abundance of Ruminococcaceae in patients with SLE decreased. It is an beneficial flora. Ruminococcaceae is belongs to Firmicutes, one of the cellulose-degrading bacteria (CDB). It can produce short-chain fatty acids (SCFA), which considered as potential orchestrators of the cross talk between gut microbiota and the host metabolism [43]. The lower relative abundance of Ruminococcaceae may lead to the imbalance of SCFA production, affecting the metabolism in human body. By studying lupus-prone mice, SCFA can inhibit B cell AID and Blimp1 expression, plasma cell differentiation, autoantibodies’ class switching, and prevent IgG1/IgG2 deposition in the kidney and prevent lupus skin lesions [44]. Therefore, the decrease in the relative abundance of Ruminococcaceae may cause some complications in patients with lupus. The study also found that SCFA can protect the integrity of the small intestinal epithelial cell membrane. The decrease of the relative abundance of Ruminococcaceae may also lead to 'leaky gut'.
The results of Meta-analysis showed that the relative abundance of Enterobacteriaceae increased after suffering from SLE. Enterobacteriaceae is one of the families of Proteobacteria, in which most of the flora have pathogenicity and can produce inflammatory reaction. For example, Enterobacteriaceae is the most common pathogen causing abdominal infection, and the extended-spectrum beta-lactamases (ESBLs) production is the main mechanism of its pathogenesis [47]. Studies have shown that high levels of fS100A8-A9 in the intestine of infants can reduce the abundance level of Enterobacteriaceae in the intestine through the expansion of Tregs, and promote the good development of the intestinal microflora [48]. It can be seen that the abundance level of Enterobacteriaceae is associated with T cells, which may be the mechanism by which changes in the abundance level of Enterobacteriaceae affect the occurrence and development of SLE. Enterobacteriaceae is also one of the main pathogens causing pulmonary infection and lung infection [49]. Increasing relative abundance of Enterobacteriacea with SLE may be one of the factors leading to multiple infections such as lung and abdominal cavity. Enterococcaceae, one of the strains of Firmicutes, is a beneficial microflora and plays a certain role in alleviating gastrointestinal damage. According to the analysis, the relative abundance of this flora in patients with SLE is higher than that in healthy people. The result might indicate that there may be bacteria can reconstruct gut homeostasis by potential compensatory regulation [42, 51]. Furthermore, there was no significant difference in Lachnospiraceae and Bacteroides between SLE patients and healthy controls in the included study.
Results of sensitivity analysis and subgroup analysis
Of the eleven studies included, six provided data on the Chao1 index. Weifang Zhu (2018) [20] was a source of heterogeneity through sensitivity analysis. Some non-antibiotic drugs can have an impact on gut microbiota taken by SLE patients, such as glucocorticoids. We found that the study includes SLE patients with newly diagnosed patients (who had not used any drugs) and revisited patients (who had used hormone or immunosuppressive therapy). But it had not recorded the amount of immunosuppressants or hormones used in every SLE patients, while the other studies had recorded that the maximum dosage of hormones used should not exceed 10 mg. It has been reported by Mengchen Guo [34] that the gut microbial of glucocorticoid treatment was similar to that of the HC group. Among the included SLE patients, the dose of prednisone was up to 20 mg, which indicated that glucocorticoid could recovered gut microbiota stability in patients with SLE. In addition, some researchers have found that when the dose of glucocorticoids in SLE patients is greater than 15mg per day with longer duration, the possibility of osteonecrosis of the femoral head will increase [52]. Hence, we suspect that the dose of corticosteroids in patients with SLE may have an impact on the results of the experiment.
After remove the article Chiara Bellocchi (2019) [18], the heterogeneity of Enterococcaceae meta was eliminated. In this study, 70.37% of the patients were taking hydroxychloroquine (HCQ), while the other three studies did not record that. A short-term treatment with high-dose or long-term use of HCQ can change gut microbiota, resulting in the decrease of relative abundance of Firmicutes [53–54]. Hence, the use of HCQ in patients with SLE may have an effect on the abundance of gut microbiota.
After omitting the study of Taco A. van der Meulen (2019) [29], the heterogeneity between Lachnospiraceae and Bacteroides was completely eliminated, which shows that this study was the source of heterogeneity of the two analysis results. We found among the thirty SLE patients included in the study, twenty-eight were White/European ethnic background, but none of the healthy controls had White/European ethnic background. In addition, none of the SLE patients were born in the Netherlands, but nine hundred twenty-nine of the nine hundred and sixty five healthy people in the control group were born in the Netherlands. Except for the influence of disease on gut microbiota, diet, environment and race also have certain effects on it [55–56]. Therefore, the environmental and ethnic differences between the experimental group and the control group will affect the results. This suggests that the conditional differences between the included controlled studies should be controlled in follow-up clinical studies.
Our subgroup analysis showed that the relative abundance of Ruminococcaceae and Enterococcaceae in patients with SLE may be affected by population. In the Chinese subgroup, Ruminococcaceae showed a significant decrease, but in the non-Chinese subgroup, this phenomenon was not prominent [33]. Several investigators analyzed gut microbiota and human genome data, and showed the influence of lineage on microbial composition [57–58]. Quantitative trait loci (QTLs) analysis was performed on Six hundred and forty-five cross-line mice, and thirteen genetic loci that were significantly related to microbial abundance were detected, further confirmed the close relationship between heredity and intestinal microorganisms. However, some research suggested selective influence of genes on gut microbiota. For example, JuliaK.Goodrich (2016) [60]. analyzed one thousand one hundred and twenty-six pairs of gut microbiota from British twins, found that the Christensenellaceae was the most highly heritable taxon. It is speculated that Ruminococcaceae and Enterococcaceae families may also be one of the strains with heredity. Therefore, the different abundance level of gut microbiota varies with different populations when suffering from SLE. Meta-analysis showed the prevalence rate of a disease increases with the increase of sample size, which indicates that the sample size has an effect on the experimental results [61]. Subgroup analysis showed there is a certain difference in the meta-analysis results of Enterobacteriaceae when the sample size was less than twenty or it was greater than twenty. This means that the impact of clinical sample size on the results of the study should be taken into account in follow-up clinical studies. When the sample size is greater than twenty, there was still some heterogeneity. Increasing the grouping may get satisfactory results. However, due to the lack of studies included in this meta-analysis, it is impossible to carry out further research.
Limitation
Whether the dose range of glucocorticoid therapy can significantly change the diversity or abundance of intestinal microorganisms has not been studied. Weifang Zhu [20] studies have shown that there is no significant statistical difference in intestinal dominant flora between SLE patients who have not been treated with drugs and SLE patients who have been treated with drugs. However, Mengchen Guo [34] pointed out that glucocorticoid therapy can regulated the balance of gut microbiota. In clinical treatment of systemic lupus erythematosus, there is a large difference in hormone dose between active stage and remission stage, so our meta-analysis lacks the changes of intestinal microorganisms in different stages of the disease, as well as the changes of gut microbiota in different periods.