The role of bacterial DNA in autoantibody induction

Alterations of the gut microbiota in the lupus nephritis: a systematic review

BACKGROUND

Emerging evidence suggests that gut microbiota dysbiosis may play a critical role in the development of lupus nephritis (LN). However, the specific characteristics of the gut microbiota in individuals with LN have not been fully clarified.

METHODS

The PubMed, Web of Science, and Embase databases were systematically searched for clinical and animal studies related to the relationship between LN and gut microbiota from inception until October 1, 2023. A semiquantitative analysis was used to assess the changes in gut microbial profiles.

RESULTS

A total of 15 clinical studies were selected for analysis, which included 138 LN patients, 441 systemic lupus erythematosus patients, and 1526 healthy controls (HCs). Five different types of LN mouse models were included in 5 animal studies. The alpha diversity was decreased in LN patients compared to HCs. A significant decrease in the Firmicutes/Bacteroidetes (F/B) ratio is considered a hallmark of pathological conditions. Specifically, alterations in the abundance of the phylum Proteobacteria, genera Streptococcus and Lactobacillus, and species Ruminococcus gnavus and Lactobacillus reuteri may play a critical role in the pathogenesis of LN. Remarkably, the gut taxonomic chain Bacteroidetes-Bacteroides-Bacteroides thetaiotaomicron was enriched in LN patients, which could be a crucial characteristic of LN patients. The increased level of interleukin-6, imbalance of regulatory T cells and T helper 17 cells, and decreased level of the intestinal tight junction proteins zonula occludens-1 and claudin-1 also might be related to the pathogenesis of LN.

CONCLUSIONS

Specific changes in the abundance of gut microbiota such as decreased F/B ratio, and the level of inflammatory indicators, and markers of intestinal barrier dysfunction may play a crucial role in the pathogenesis of LN. These factors could be effective diagnostic and potential therapeutic targets for LN.

Gut Microbiota in Systemic Lupus Erythematosus and Correlation With Diet and Clinical Manifestations

Despite the existing studies relating systemic lupus erythematosus (SLE) to changes in gut microbiota, the latter is affected by external factors such as diet and living environment. Herein, we compared the diversity and composition of gut microbiota in SLE patients and in their healthy family members who share the same household, to link gut microbiota, diet and SLE clinical manifestations. The study cohort included 19 patients with SLE and 19 of their healthy family members. Daily nutrition was assessed using a food frequency questionnaire (FFQ). Microbiota was analyzed using amplicons from the V4 regions of the 16S rRNA gene, to obtain microbiota diversity, taxa relative abundances and network analysis. The gut microbiota in the SLE group had lower alpha diversity and higher heterogeneity than the control group. SLE patients had decreased Acidobacteria, Gemmatimonadetes, Nitrospirae and Planctomycetes at the phylum level, and increased Streptococcus, Veillonella, Clostridium_XI, and Rothia at the genus level. Streptococcus was extremely enriched among patients with lupus nephritis. Lactobacillus, Clostridium_XlVa, Lachnospiracea_incertae_sedis and Parasutterella OTUs were associated with diet and clinical features of SLE. Finally, the gut microbiota of SLE patients remained different from that in healthy controls even after accounting for living conditions and diet.

Acquired infantile abducens palsy associated with anti-GM2 antibodies

Anti-ganglioside antibodies have been associated with acquired neuropathies, including Guillain-Barré syndrome. We describe a case of acute abducens nerve palsy acquired 2 weeks after symptoms of upper respiratory tract infection and rash in a 6-month-old. Elevated anti-GM2 ganglioside immunoglobulin M antibodies were detected in the serum. The palsy slowly improved over time, although eventually surgical intervention was required. Elevated anti-GM2 immunoglobulin M antibodies have previously been reported in Guillain-Barré syndrome variants involving sensory and cranial neuropathies, but never in isolated unilateral cranial nerve VI mononeuropathy. Anti-ganglioside antibodies may play a role in the pathogenesis of postinfectious isolated abducens palsy in young children.

SLE—a disease of clearance deficiency?

Systemic lupus erythematosus (SLE) is a multifactorial disease and its pathogenesis and precise aetiology remain unknown. Under physiological conditions, neither apoptotic nor necrotic cell material is easily found in tissues because of its quick removal by a highly efficient scavenger system. Autoantigens are found in apoptotic and necrotic material and they are recognized by autoimmune sera from SLE patients. The clearance of dying cells is finely regulated by a highly redundant system of receptors on phagocytic cells and bridging molecules, which detect molecules specific for dying cells. Changes on apoptotic and necrotic cell surfaces are extremely important for their recognition and further disposal. Some SLE patients seem to have an impaired ability to clear such apoptotic material from tissues, and this could cause the breakdown of central and peripheral mechanisms of tolerance against self-antigens. In this article, we address the cells, receptors and molecules involved in the clearance process and show how deficiencies in this process may contribute to the aetiopathogenesis of SLE.

Autoreactive responses to an environmental factor. 2. Phthalate-induced anti-DNA specificity is downregulated by autoreactive cytotoxic T cells

An environmental factor (phthalate) was shown, in our previous study, to induce serum anti-DNA responses in BALB/c, NZB and lupus-prone NZB/W F1 mice. Out of such anti-phthalate responses, cross-reactive populations were identified that strongly bind phthalate, DNA, or both. A phthalate-specific BALB/c monoclonal antibody, 2C3-Ig (gamma1,kappa), showed considerable affinity for DNA and had extensive sequence homology with the heavy and light chain variable regions of a known anti-DNA immunoglobulin, BV04-01, from lupus-prone NZB/W F1 mice. This study was initiated to address how BALB/c mice, but not NZB/W F1 mice, are protected from these adverse autoreactive B cells. Using 2C3 hybridoma cells as the prototype autoreactive BALB/c B cell, we determined whether its DNA-binding monoclonal antibody would induce any regulatory cell-mediated immune responses. Synthetic idiopeptides corresponding to the heavy and light chain variable regions of 2C3-Ig were found to be effective at inducing specific effector cells in BALB/c mice, but not in lupus-prone F1 mice. The splenocytes from BALB/c mice incubated in vitro with the idiopeptides, particularly the complementarity-determining region 1 (VL1) of the 2C3-Ig light chain, showed significant proliferative and cytolytic responses. A CD8+ cytotoxic T-lymphocyte (CTL) response was elicited that recognized the VL1 peptide presented by the Kd allele, and affected the growth of 2C3 cells. In vivo depletion of CD8+ T cells in BALB/c mice significantly decreased this CTL activity but increased the anti-DNA humoral response. These results suggest that autoreactive CTLs are induced in non-autoimmune prone mice as a mechanism to downregulate self-reactive B cells.

Autoreactive responses to an environmental factor: 1. phthalate induces antibodies exhibiting anti-DNA specificity

Environmental factors have been implicated in the induction of autoimmune disorders. We report here that a common chemical, phthalate, used widely in synthetic polymers and cosmetics induces serum anti-self DNA antibodies in BALB/c, NZB and autoimmune-prone NZB/W F1 mice. The latter group experiences a high mortality, and significantly higher anti-DNA antibody levels along with nephritis and other histopathologic changes in kidney. Comparison of amino acid sequences of an anti-phthalate BALB/c B-cell hybrid, 2C3 with the known database at the National Center for Biotechnology Information reveals a striking homology between the variable regions of 2C3-Ig (gamma1, kappa) and an anti-DNA antibody, BV04-01 (gamma2b,kappa) isolated from the lupus-prone NZB/W F1 mice. The homology is 98% for kappa light chain and 70% for gamma heavy chain. Like 2C3-Ig, BV04-01 also has specificity for d(pT)4. Furthermore, the light chains of both 2C3-Ig and BV04-01 are products of Vkappa1 gene. To understand the nature of anti-phthalate responses in general, hybridomas generated from phthalate-keyhole limpet haemocyanin-primed BALB/c splenocytes were characterized. The study identifies cross-reactive populations that strongly bind phthalate, DNA, or both. Of the 14 hybridomas evaluated, six express the same Vkappa1 gene-derived light chain as 2C3, and bind both phthalate and ds and ss-DNA. They specifically recognize the oligonucleotides, d(pT)4, and d(pT)10. Additionally, when antisera raised against idiopeptides corresponding to 2C3-Ig hypervariable regions are allowed to react with 2C3-Ig, their binding is blocked specifically by both d(pT)4 and phthalate. This study clearly demonstrates that phthalate exposure leads to activation of a significant number of autoreactive B-cells, with the consequence of a significant pathogenic progression in susceptible NZB/W F1 mice but not in non-autoimmune-prone BALB/c.

Retrospective seroepidemiological survey for human babesiosis in an area in Japan where a tick-borne disease is endemic

A total of 1,335 archived human sera collected in 1985 from an area in Japan where a tick-borne disease is endemic were examined by indirect immunofluorescence antibody test (IFAT) to estimate seroprevalence against three serologically distinct types of Babesia microti-like parasites; namely, Hobetsu, Kobe, and U.S. types. Eighteen sera (1.3%) were found to be IFAT-positive (titer 1:100-1:6,400), of which 14 and three were ascertained by Western blot analysis to be positive against the Hobetsu and Kobe types, respectively. In addition, four sera showed an IFAT titer of 1:100 against the U.S. type, but they appeared to be false-positive because they were cross-reactive against the Hobetsu and Kobe types, and also because a U.S.-type parasite has not been found in Japan. Our results suggest that human babesiosis in Japan occurred prior to the discovery of the index case in 1999 and that the infections were caused mainly by Hobetsu-type parasites.

Complexes of serum amyloid P component and DNA in serum from healthy individuals and systemic lupus erythematosus patients

Serum amyloid P component (SAP) binds in vitro to DNA; based on findings in SAP-deficient mice it was proposed that SAP's role is to handle chromatin and DNA, thereby preventing formation of anti-DNA antibodies. For the first time we have shown the presence of Ca2+-dependent SAP-DNA complexes, measured by ELISA, in sera from both healthy volunteers and systemic lupus erythematosus patients (SLE). The concentration of SAP-DNA complexes in SLE sera was significantly lower than in normal sera and particularly low in sera from patients with anti-DNA titers exceeding 50. The complexes were dissociated by the SAP ligand heparin and were not demonstrable in EDTA plasma. Normal sera showed similar capacity to form SAP-DNA complexes with both thymus and Escherichia coli DNA, whereas significantly lower amounts of complexes, in particular with E. coli DNA, were formed in SLE sera. SLE patients with moderate to high anti-DNA titers showed a significant negative correlation between serum SAP's binding of E. coli DNA and the anti-DNA titer.