Objective Systemic lupus erythematosus (SLE) is characterized by the production of antibodies against self antigens. However, the events underlying autoantibody formation in SLE remain unclear. This study was undertaken to investigate the role of plasma autoantibody levels, microbial translocation, and the microbiome in SLE. Methods Plasma samples from 2 cohorts, one with 18 unrelated healthy controls and 18 first‐degree relatives and the other with 19 healthy controls and 21 SLE patients, were assessed for autoantibody levels by autoantigen microarray analysis, measurement of lipopolysaccharide (LPS) levels by Limulus amebocyte assay, and determination of microbiome composition by microbial 16S ribosomal DNA sequencing. Results First‐degree relatives and SLE patients exhibited increased plasma autoantibody levels compared to their control groups. Parents and children of lupus patients exhibited elevated plasma LPS levels compared to controls (P = 0.02). Plasma LPS levels positively correlated with plasma anti–double‐stranded DNA IgG levels in first‐degree relatives (r = 0.51, P = 0.03), but not in SLE patients. Circulating microbiome analysis revealed that first‐degree relatives had significantly reduced microbiome diversity compared to their controls (observed species, P = 0.004; Chao1 index, P = 0.005), but this reduction was not observed in SLE patients. The majority of bacteria that were differentially abundant between unrelated healthy controls and first‐degree relatives were in the Firmicutes phylum, while differences in bacteria from several phyla were identified between healthy controls and SLE patients. Bacteria in the Paenibacillus genus were the only overlapping differentially abundant bacteria in both cohorts, and were reduced in first‐degree relatives (adjusted P [Padj] = 2.13 × 10−12) and SLE patients (Padj = 0.008) but elevated in controls. Conclusions These results indicate a possible role of plasma microbial translocation and microbiome composition in influencing autoantibody development in SLE.

Progesterone plays a protective role in preventing inflammation and preterm delivery during pregnancy. However, the mechanism involved is unknown. Microbial product translocation from a permeable mucosa is demonstrated as a driver of inflammation. To study the mechanism of the protective role of progesterone during pregnancy, we investigated the effect of physiologic concentrations of progesterone on tight junction protein occludin expression and human gut permeability in vitro and systemic microbial translocation in pregnant women in vivo . Plasma bacterial lipopolysaccharide (LPS), a representative marker of in vivo systemic microbial translocation was measured. We found that plasma LPS levels were significantly decreased during 24 to 28 weeks of gestation compared to 8 to 12 weeks of gestation. Moreover, plasma LPS levels were negatively correlated with plasma progesterone levels but positively correlated with plasma tumor necrosis factor-alpha (TNF-α) levels at 8 to 12 weeks of gestation but not at 24 to 28 weeks of gestation. Progesterone treatment increased intestinal trans-epithelial electrical resistance (TEER) in primary human colon tissues and Caco-2 cells in vitro through upregulating tight junction protein occludin expression. Furthermore, progesterone exhibited an inhibitory effect on nuclear factor kappa B (NF-κB) activation following LPS stimulation in Caco-2 cells. These results reveal a novel mechanism that progesterone may play an important role in decreasing mucosal permeability, systemic microbial translocation, and inflammation during pregnancy.

Blood microbiome is important to investigate microbial-host interactions and the effects on systemic immune perturbations. However, this effort has met with major challenges due to low microbial biomass and background artifacts. In the current study, microbial 16S DNA sequencing was applied to analyze plasma microbiome. We have developed a quality-filtering strategy to evaluate and exclude low levels of microbial sequences, potential contaminations, and artifacts from plasma microbial 16S DNA sequencing analyses. Furthermore, we have applied our technique in three cohorts, including tobacco-smokers, HIV-infected individuals, and individuals with systemic lupus erythematosus (SLE), as well as corresponding controls. More than 97% of total sequence data was removed using stringent quality-filtering strategy analyses; those removed amplicon sequence variants (ASVs) were low levels of microbial sequences, contaminations, and artifacts. The specifically enriched pathobiont bacterial ASVs have been identified in plasmas from tobacco-smokers, HIV-infected individuals, and individuals with SLE but not from control subjects. The associations between these ASVs and disease pathogenesis were demonstrated. The pathologic activities of some identified bacteria were further verified in vitro. We present a quality-filtering strategy to identify pathogenesis-associated plasma microbiome. Our approach provides a method for studying the diagnosis of subclinical microbial infection as well as for understanding the roles of microbiome-host interaction in disease pathogenesis.

Background Increased autoreactive antibodies have been reported in HIV disease; however, the mechanism accounting for autoantibody induction in HIV remains unknown. Results Herein, we show that seasonal influenza vaccination induces autoantibody production (e.g., IgG anti-nuclear antibody (ANA) and anti-double-stranded DNA antibody (anti-dsDNA)) in some viral-suppressed antiretroviral therapy (ART)-treated HIV+ subjects, but not in healthy controls. These autoantibodies were not derived from antigen-specific B cells but from activated “bystander” B cells analyzed by single-cell assay and by study of purified polyclonal ANAs from plasma. To explore the mechanism of autoantibody generation in HIV+ subjects, plasma level of microbial products, gene expression profile of B cells, and B cell receptor (BCR) repertoires were analyzed. We found that autoantibody production was associated with increased plasma level of microbial translocation; the patients with high autoantibodies had skewed B cell repertoires and upregulation of genes related to innate immune activation in response to microbial translocation. By analyzing circulating microbial 16S rDNA in plasma, the relative abundance of Staphylococcus was found to be associated with autoantibody production in HIV+ subjects. Finally, we found that injection of heat-killed Staphylococcus aureus promoted germinal center B cell responses and autoantibody production in mice, consistent with the notion that autoantibody production in HIV+ patients is triggered by microbial products. Conclusions Our results showed that translocation of Staphylococcus can promote B cell activation through enhancing germinal center response and induces autoantibody production. It uncovers a potential mechanism linking microbial translocation and autoimmunity in HIV+ disease and provides a strong rationale for targeting Staphylococcus to prevent autoantibody production. Electronic supplementary material The online version of this article (10.1186/s40168-019-0646-1) contains supplementary material, which is available to authorized users.

Although effective antiretroviral therapy (ART) suppresses HIV viral replication, prevents AIDS-related complications, and prolongs life, a proportion of patients fails to restore the patients' CD4 T cell number to the level of healthy individuals. Increased mortality and morbidity have been observed in these patients. In the current study, we have investigated the role of auto-IgGs in CD4 T cell apoptosis and recovery in a cross-sectional study. All HIV subjects were on viral-suppressive ART treatment with a different degree of CD4 T cell reconstitution. Total auto-IgG binding on CD4 T cell surfaces and its associated apoptosis and CD4 T cell recovery were analyzed by flow cytometry ex vivo. Total IgGs from plasma were tested for their binding capacities to CD4 T cell surfaces and their mediation to CD4 T cell death through NK cell cytotoxicity in vitro. HIV subjects had increased surface binding of auto-IgGs on CD4 T cells compared with healthy controls, and IgG binding was associated with elevated CD4 T cell apoptosis in HIV subjects but not in healthy controls. Plasma IgGs from HIV subjects bound to CD4 T cells and induced cell apoptosis through NK cytotoxicity in vitro. Soluble CD4 (sCD4) preincubation prevented NK cell-mediated CD4 T cell death. Our results suggest that plasma autoantibodies may play a role in some HIV patients with poor CD4 T cell recovery under viral-suppressive ART.