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Systemic lupus erythematosus (SLE) is a multi-system autoimmune disease. The cause of SLE is not only genetic; in fact, environmental factors may play a more important role in disease development. The MRL/lpr mouse model lupus-like symptoms due to multiple SLE susceptible loci in the MRL background, and offers an accelerated model compared to the MRL parent strain due to the Faslpr mutation. Recently, our laboratory witnessed a loss of disease phenotype in our in-house colony of MRL/lpr mice. We thus compared mice newly obtained from The Jackson Laboratory (JAX; Stock Number 000485) to our in-house mice. The single-nucleotide polymorphism (SNP) analysis showed no genetic drift, suggesting that environmental factors could be triggering a phenotypic drift. Surprisingly, the newly purchased JAX mice also had attenuation of glomerulonephritis. Even though JAX mice manifested similar attenuation of lupus nephritis, our in-house colony showed differences in organ weights. Furthermore, males showed a significantly higher level of anti-double stranded DNA auto-IgG consistent with germinal center maturation. In addition, in-house males had significantly higher levels of microRNA-21 and microRNA-183 explaining spleen size difference. Moreover, the composition of gut microbiota was different between in-house and new JAX mice at early age, with many groups of bacteria differing at later time points, which might explain some of the phenotypic differences. These results suggest that microRNAs and gut microbiota might be responsible for the phenotypic differences of MRL/lpr mice in JAX and our colonies as they were genetically identical. On the other hand, the attenuation of nephritis in both groups requires further investigation. Supported by R01AR073240

Systemic Lupus Erythematosus(SLE), a disease of various genetic and environmental origins, is often characterized by immune complexes causing inflammation and damage in various organ systems, such as the brain, kidneys, lung, joint, and skin. Current treatment for SLE include steroidal and nonsteroidal anti-inflammatory drugs, antimalarial agents, and immunosuppressive medications. These treatments primarily reduce symptoms, and patients may develop side effects with long-term care. The gut microbiome has an important role in various metabolic and immunological diseases. A previous study found that increased Lactobacillus colonization restored the mucosal barrier, and increased abundance in these bacteria attenuated SLE symptoms through reversing a ‘leaky gut’. This allows for potential therapies of SLE with probiotics. In preliminary trials, vancomycin treatment during active disease killed gram-positive bacteria, but spared Lactobacillus, and attenuated symptoms. Surprisingly, significantly decreased amounts of CD10+CD19+ B cells that produce IL-10 (B10) were found when vancomycin was given before the onset of lupus. Vancomycin treatment before disease onset significantly removed bacterial DNA from the gut and circulation, causing exacerbation of clinical symptoms. Oral gavage of activated B10 cells in vancomycin treated mice rescued the negative effects of vancomycin treated mice at the pre-disease stage. This work suggests that a form of oral tolerance induced by bacterial DNA-mediated expansion of B10 cells suppress disease onset in the autoimmune-prone MRL/lpr mouse model. Future studies are warranted to further define the mechanism behind bacterial DNA promoting B10 cells.

Systemic lupus erythematosus (SLE) is a multi-system autoimmune disease with no known cure. Gut microbiota and the immune system have a close relationship that controls inflammation. Alterations in the gut microbiota, known as dysbiosis, can trigger SLE in both human and mouse. We previously published differences between the gut microbiota in lupus-prone MRL/Mp-Faslpr (lpr) mice compared to healthy controls, with lower Lactobacillaceae abundance in lpr mice. Restoring the gut microbiota with a mix of 5 different strains of this family significantly attenuated lupus-liked disease in lpr mice. In this study, we sought to understand the potential benefit of this mix in lpr mice with Cx3cr1 deficiency (KO). KO mice on C57BL/6 background display increased translocation of commensal bacteria into the mesenteric lymph node (MLN) and increased susceptibility to intestinal inflammation. However, whether CX3CR1+ macrophages play a role in controlling systemic inflammation was unclear. After backcrossing the KO allele to lpr mice, we found that KO lpr mice exhibited exacerbated splenomegaly and lymphadenopathy, as well as increased proteinuria. Interestingly, treating the KO lpr mice with the 5 Lactobacillus strains attenuated the enlargement of MLN and abrogated the increase of proteinuria. Furthermore, the effects of the probiotic bacteria were accompanied by downregulation of serum endotoxin, suggesting the reversal of a leaky gut that may explain their benefits on KO lpr mice. Together, our results show an important role of CX3CR1+ macrophages in controlling systemic inflammation in lupus, and that probiotic Lactobacillus spp. may be an effective treatment against SLE through preventing bacterial translocation.

Vitamin A deficiency (VAD) is observed in both human and mice with lupus nephritis (LN). However, whether VAD is a driving factor for LN progression is unclear. Here, we investigated the effect of VAD on the progression of LN in a lupus-prone mouse model, MRL/lpr. In these mice, while LN is not apparent before 8 weeks of age, the inflammation of lymphoid tissues suggesting initiation of lupus is evident at weaning. Thus, we initiated VAD either before or after weaning to reveal a potential time-dependent effect. At around 15 weeks of age with both types of VAD, we found exacerbated LN that was characterized by deteriorated kidney inflammation, impaired renal epithelial integrity, and dramatic squamous metaplasia of the renal pelvic urothelium. Both types of VAD provoked severe neutrophilic tubulointerstitial nephritis and accelerated renal failure. This was concomitant with significantly higher mortality in all VAD mice. Looking at an earlier time point of 7 weeks of age and before the onset of clinical LN, both types of VAD increased splenomegaly, lymphadenopathy, and circulating autoantibodies; three additional hallmarks of lupus, as well as renal infiltration of conventional and plasmacytoid dendritic cells. These results suggest VAD-driven deterioration of LN regardless of the time of VAD initiation. Our findings raise significant public health concerns that concurrent lupus and VAD may lead to more severe SLE. Future studies will elucidate the underlying mechanisms of how VAD modulates myeloid cells to accelerate the initiation of LN.

Hypersensitivity reactions and immune dysregulation have been reported with the use of quaternary ammonium compound disinfectants (QACs). We hypothesized that QAC exposure would exacerbate autoimmunity associated with systemic lupus erythematosus (lupus). Surprisingly, however, we found that compared to QAC-free mice, ambient exposure of lupus-prone mice to QACs led to smaller spleens with no change in circulating autoantibodies or the severity of glomerulonephritis. This suggests that QACs may have immunosuppressive effects on lupus. Using a microfluidic device, we showed that ambient exposure to QACs reduced directional migration of bone marrow-derived neutrophils toward an inflammatory chemoattractant ex vivo. Consistent with this, we found decreased infiltration of neutrophils into the spleen. While bone marrow-derived neutrophils appeared to exhibit a pro-inflammatory profile, upregulated expression of PD-L1 was observed on neutrophils that infiltrated the spleen, which in turn interacted with PD-1 on T cells and modulated their fate. Specifically, QAC exposure hindered activation of splenic T cells and increased apoptosis of effector T-cell populations. Collectively, these results suggest that ambient QAC exposure decreases lupus-associated splenomegaly likely through neutrophil-mediated toning of T-cell activation and/or apoptosis. However, our findings also indicate that even ambient exposure could alter immune cell phenotypes, functions, and their fate. Further investigations on how QACs affect immunity under steady-state conditions are warranted. National Institute of Arthritis and Musculoskeletal and Skin DiseasesUnited States Department of Health & Human ServicesNational Institutes of Health (NIH) - USANIH National Institute of Arthritis & Musculoskeletal & Skin Diseases (NIAMS); National Institute of Environmental Health SciencesUnited States Department of Health & Human ServicesNational Institutes of Health (NIH) - USANIH National Institute of Environmental Health Sciences (NIEHS) [T32-ES007032]; National Institute of General Medical Sciences of the National Institutes of HealthUnited States Department of Health & Human ServicesNational Institutes of Health (NIH) - USANIH National Institute of General Medical Sciences (NIGMS) [R35GM133610] Funding was received from National Institute of Arthritis and Musculoskeletal and Skin Diseases. We also would like to acknowledge the following funding sources. Environmental Pathology and Toxicology Training Grant funded by the National Institute of Environmental Health Sciences (T32-ES007032) for supporting RP. Seguin. The National Institute of General Medical Sciences of the National Institutes of Health under award number R35GM133610 for supporting M Moarefian.

Maternal factors play an essential role in shaping the immune system of the newborn, yet it is unknown whether maternal factors could modulate the development of systemic lupus erythematosus (SLE) in the offspring. Activation-induced cytidine deaminase (AID) is an enzyme required for somatic hypermutation and class switch recombination. Given that IgG and IgA isotypes account for the vast majority of passive immunity in rodents, our previously established AID-deficient BXSB mice provide a model in which no IgG or IgA antibodies are transferred to the offspring. In this study, we compared genotypically identical mice born to either AID-sufficient dams or AID-deficient dams and evaluated the effects of maternal antibodies in disease progression. Offspring from knockout dams developed disease at a faster rate, as shown by more severe nephritis and elevated pathogenic autoantibodies compared to their counterparts born to wild type dams. In addition, the splenic structure was intensively disrupted with disorganized follicles and fewer discernible germinal centers. A more activated T cell phenotype was also characterized in maternal antibody-deficient mice. When immune competent pups were cross-fostered onto AID deficient dams, these mice exhibited more severe disease phenotypes, indicating the protective antibody effect contributes to the modulation of SLE progression in post-natal period. Overall, these findings highlight the importance of maternal antibodies in programming the immune system and altering the SLE development in the offspring.

We previously showed that all-trans-retinoic acid (tRA) exacerbated pre-existing autoimmunity in lupus; however, its effects before disease onset are unknown. Here, using a pristane-induced model, we show that tRA exerts tissue-specific effects when given at the initiation vs. continuation phase of lupus. Pre-pristane treatment with tRA aggravated glomerulonephritis through increasing renal expression of pro-fibrotic protein laminin β1, activating bone marrow CD11b- conventional dendritic cells, increasing the splenic CD4:CD8 ratio, and upregulating the interaction of ICAM-1 and LFA-1 that led to the infiltration of inflammatory cells to the spleen. Transcriptomic analysis revealed that prior to lupus induction, tRA significantly upregulated genes associated with cell differentiation, activation, and migration. Moreover, compared to pristane alone, tRA pre-treatment potentiated, whereas tRA post-treatment significantly suppressed, the renal expression of proinflammatory TNF-α, IL-1β, CCL2, and CCL3. While it may benefit the kidney, post-pristane treatment with tRA worsened the onset and severity of pristane-induced arthritis through promoting neutrophil and mononuclear cell infiltration into the joints. Together, these findings suggest that tRA supplementation regardless of the time of administration promotes chemokine-driven migration and tissue-specific infiltration of inflammatory cells, thereby exacerbating lupus-associated kidney or joint inflammation. Interestingly, both pre- and post-treatments with tRA modulated the gut microbiota in a similar fashion, suggesting a gut microbiota-independent mechanism by which tRA affects the initiation vs. continuation phase of lupus.

Dysbiosis in the gut microbiota has been observed in a various autoimmune disease, including SLE, which could cause a leaky gut, triggering an immune response, and thus worsening autoimmune disease expression. In our current studies, we hypothesized that increasing dietary fiber would create a healthy microbiota environment in the gut, leading to decreased leakiness of the gut and to decreased disease expression in and NZB/NZW female mice. NZB/NZW mice were placed on standardized high fiber (HF 30%) or low fiber (LF 0.4%) for 12 weeks beginning at 10 weeks of age. Mice were assessed as they aged for various parameters of disease including proteinuria and anti-dsDNA antibody production. Alteration of the microbiota and short chain fatty acid levels were also assessed. At 36 weeks-of-age, the mice were euthanized and we assessed occlusion protein expression, splenocyte profiles, and kidney tissue. We found as the mice aged, their body weights, anti-dsDNA antibody levels, and proteinuria were not significantly different between the groups. Similarly, there were no differences in SCFA levels. In regard to the microbiota, Chlostridiales bacteria were consistently increased in the HF treated mice compared to the LF treated mice. In regard to disease progression, spleen weight, immune cell profiles, proteinuria, dsDNA levels, and kidney pathology, there was no difference between the HF and LF treated groups. Taken together, these results indicate that in the NZB/W female mouse, a HF diet may alter the microbiota but does not influence disease progression.

Systemic lupus erythematosus (SLE) is a multi-system autoimmune disease with no known cure. The role of gut microbiota and its interaction with the immune system can direct tolerance induction to self-antigens not only in the intestinal mucosa but also at the systemic level. Our lab previously showed differences between the gut microbiota in lupus-prone MRL/Mp-Faslpr (lpr) mice compared to healthy controls, with lower Lactobacillaceae levels in lpr mice. Restoring the microbiota with a mix of 5 different Lactobacillus strains, L. reuteri, L. oris, L. johnsonii, L. gasseri, and L. rhamnosus significantly attenuated lupus-liked disease in lpr mice, by increasing regulatory T cells and balancing T helper-17 cells. Interestingly, we found L. reuteri and an uncultured Lactobacillus spp. were present based on 16S rRNA sequencing. To evaluate the effect of the main candidate L. reuteri in attenuating lupus, we treated lpr mice with the single bacterial strain. Surprisingly, L. reuteri did not reproduce the same results as the Lactobacillus mixture. Thus, we tested the remaining strains individually but none was able to recapitulate the effect of the 5 strains. Additionally, we treated lpr mice with the supernatant of the 5 strains containing secreted metabolites, which did not significantly attenuate lupus. These results suggest that communications among different strains of lactobacilli may be required in ameliorating the disease. Probiotic Lactobacillus spp. may be an alternative treatment against SLE, but further investigations are warranted to delineate the mechanisms of how multiple strains of lactobacilli can exert a beneficial effect as a community.

SLE is a complex autoimmune disorder with no known cure. We previously reported that oral vancomycin treatment of female MRL/lpr mice during active disease (9 to 15 weeks of age) could significantly ameliorate disease symptoms. However, when vancomycin treatment was initiated from an earlier age (from 3 to 15 weeks), the beneficial effect was not observed. Strikingly, mice given vancomycin during the pre-disease stage (from 3 to 8 weeks) exhibited exacerbated lupus disease. As vancomycin works by removing parts of the gut microbiota, we hypothesized that the regulatory immunity induced by gut microbiota at early age is essential in hammering lupus disease development in MRL/lpr mice. To test the hypothesis, we analyzed diverse regulatory cell types from the mice receiving vancomycin from 3 to 8 weeks of age. Regulatory B (Breg) cells, in particular, were found to be reduced in both the percentage and absolute number in multiple lymphoid organs. Importantly, adoptive transfer of Breg cells at 6–7 weeks of age to long-term vancomycin-treated mice improved lupus-like symptoms. This clearly indicates that Breg cells, inducible by vancomycin-sensitive gut microbiota, plays an important role in suppressing lupus disease initiation and progression. We next sought to determine Breg inducers in the gut microbiota. The serum level of bacterial DNA was found to be significantly lower in mice treated with vancomycin. More importantly, early administration of bacterial DNA reproduced the beneficial effect seen in the Breg adoptive transfer experiment. Together, these results suggest an important protective mechanism against lupus initiation that involves bacterial DNA in the gut microbiota and the induction of Breg cells.

Dysbiosis of gut microbiota exists in the pathogenesis of many autoimmune diseases, including lupus. Currently, women with lupus are recommended to avoid pregnancy, as lupus patients who experienced pregnancy usually had more severe disease flares. However, the possible role of gut microbiota in the link between pregnancy and exacerbation of lupus remains to be explored. In the present study, in the classical lupus mouse model MRL/lpr, we compared the structures of gut microbiota in pregnant and lactating individuals vs. age-matched naïve mice. Consistent with studies on non-lupus mice, both pregnancy and lactation significantly changed the composition and diversity of gut microbiota. Strikingly, modulation of gut microbiota using the same strategy resulted in different disease outcomes in experienced (which had undergone pregnancy and lactation) vs. control (naïve) MRL/lpr females: while vancomycin treatment attenuated lupus in naïve mice, it even exacerbated lupus in experienced mice. L. animalis flourished in the gut upon vancomycin treatment, and direct administration of the bacteria recapitulated the differential effects of vancomycin in experienced vs. control mice. A pregnancy-related enzyme, DHNA, was significantly inhibited by L. animalis; however, this inhibition was only apparent in experienced mice, which explained, at least partially, the lack of beneficial response to vancomycin in these mice. The differential production of IL-10 and IFNγ in experienced vs. control mice further explained why the disease phenotypes varied between the two types of mice bearing the same treatment. These results suggest that pregnancy and lactation interfere with the response of autoimmunity to modulation of gut microbiota.

Maternal microbiota plays a key role in governing the establishment of neonatal gut microbiota. However, whether and how maternal microbiota from breast milk would affect the development of neonatal immune response remains unclear. Here we report that de novo synthesis of neonatal IgA in pre-weaning Rag1-sufficient mouse pups could be super-induced by the milk of Rag1−/− nursing moms. 16S rRNA sequencing analysis showed that the gut microbiota from the upper intestine of Rag1-sufficient pups were distinct depending on the genotypes of their nursing moms, with those nursed by Rag1−/− moms exhibiting a higher bacterial diversity than those nursed by Rag1-sufficient moms. Interestingly, when Rag1−/− moms were co-housed (littermates) with Rag1-sufficient moms, or treated with antibiotics, the pups that they nursed no longer exhibited the heightened IgA synthesis. Further studies revealed that the number of type 3 innate lymphoid cells (ILC3s) in the pups’ intestine was significantly increased when the pups were nursed by Rag1−/− moms. In addition, the super-induction of neonatal IgA was abrogated when pups were treated with an aryl hydrocarbon receptor antagonist that is known to reduce the number and function of ILC3s. These results suggest that the maternal microbiota may educate neonatal IgA response through an ILC3-dependent mechanism.

Histone deacetylase 6 (HDAC6) is a Class IIb HDACs enzyme primarily residing in the cytoplasm. HDAC6 alters gene transcription by removing acetyl groups from lysine residues on transcription factors. We, and others, have previously demonstrated that HDAC6 expression is increased in systemic lupus erythematosus (SLE) patients and animal models of lupus and that inhibition of HDAC6 decreased disease. In our current studies, we tested if an orally active selective HDAC6 inhibitor would decrease disease pathogenesis in a lupus mouse model with established early disease. Importantly, we sought to delineate the cellular and molecular mechanism(s) of action for the HDAC6 inhibitor. We treated 20-week-old early-diseased NZB/W F1 (lupus) female mice with two different doses of the selective HDAC6 inhibitor (ACY-738) for five weeks. At the termination of the study, our results showed a reduced germinal center B cell response, decreased T follicular helper cells and diminished IFN-g production from T helper cells in splenic tissue. Additionally, we found the IFNa-producing ability of plasmacytoid dendritic cells was decreased along with immunoglobulin isotype switching and the generation of pathogenic autoantibodies. Renal tissue showed decreased immunoglobulin deposition and reduced inflammation as judged by glomerular and interstitial inflammation. Taking together, these studies show selective HDAC inhibition decreased several parameters of disease pathogenesis in lupus prone mice. The decrease was in part due to inhibition of autoreactive B cell differentiation. Studies are currently underway to define further the mechanism of how HDAC6 inhibits auto-reactive B cell differentiation.

Lupus nephritis, a leading cause of morbidity and mortality in patients with Systemic Lupus Erythematosus (SLE), manifests as inflammatory infiltration of the kidney. Many types of leukocytes infiltrate the kidney during the progression of lupus nephritis, but the specific contributions of each infiltrating population are still unclear. In this study, we have found that CD11c+cells accumulate in nephritic kidneys of lupus-prone mice. These renal CD11c+ cells, forming clusters with infiltrating T cells, are proinflammatory and secreting cytokines that promote autoantibody production and Th17 response. They also produce chemokines that attract other leukocytes into the kidney. The surface phenotype (CD11b+CD115highCD135lowCX3CR1highFcgRIVhigh)suggests that they may be derived from mature monocytes and be activated by pathogenic immune complexes. Ex vivo co-culture experiments also suggest that they can maintain the survival of renal infiltrating T cells. To further demonstrate the role of these CD11c+ cells in vivo, we are currently depleting them by targeting CX3CR1, as they are a unique population of cells predominantly expressing a high level of CX3CR1. The results obtained from this study will be important for the understanding of lupus pathogenesis and identification of new therapeutic targets against lupus nephritis.

Gut microbiota and the immune system interact to maintain tissue homeostasis, but whether this interaction is involved in the pathogenesis of systemic lupus erythematosus (SLE) is unclear. Rheumatologists and patients have observed that antibiotics can control lupus flares, suggesting a role for pathogenic microflora in SLE. Here we report that oral antibiotics given during active disease removed harmful bacteria from the gut microbiota and attenuated lupus. Using MRL/lpr mice, we showed that antibiotics ameliorated systemic autoimmunity and kidney histopathology. They also decreased IL-17-producing cells and increased the level of circulating IL-10. In addition, antibiotics removed Lachnospiraceae and increased the relative abundance of Lactobacillus spp., two groups of bacteria previously shown to be associated with deteriorated or improved symptoms in MRL/lpr mice, respectively. Furthermore, we showed that the attenuated disease phenotype could be recapitulated with a single antibiotic vancomycin, suggesting the use of vancomycin as a potential treatment in SLE.

Plasmacytoid dendritic cells (pDCs) are professional type I IFN producers believed to promote lupus. However, questions exist about whether they function at the same level throughout the course of lupus disease. We analyzed high-purity pDCs sorted from lupus mice. Although pDCs produced a large amount of IFN-α during disease initiation, those sorted from late-stage lupus mice were found to be defective in producing IFN-α. These pDCs expressed an increased level of MHC, suggesting a functional drift to Ag presentation. We examined the potential mechanism behind the defect and identified a novel transcriptional factor, Foxj2, which repressed the expression of several genes in pDCs, but not IFN-α. Dysregulation in pDCs appears to be predisposed, because they exhibited an altered transcriptional profile before the onset of clinical signs. Our results suggest that pDCs do not function the same throughout the disease course and lose the ability to produce IFN-α in late-stage lupus mice.

Systemic lupus erythematosus (SLE), a systemic autoimmune disease, involves mild to severe manifestations in multiple organs. Currently, lupus-prone mouse models are used to understand the mechanisms of SLE development and discover new therapies. However, due to differences between rodents and humans, such as physiological development, disease progression, and response to therapies and drugs, many mechanisms and therapies discovered in mice may not be efficiently transferred from murine lupus models to SLE patients. Here we present a humanized mouse model of lupus as a new technology to bridge the gap between rodent models and patients. In our model, which involves vigorous selection of donors, we engraft peripheral blood mononuclear cells (PBMCs) from SLE patients into NOD/SCID/IL2Rgnull (NSG) mice to build a human-specific disease-based immune system in the mice. To avoid graft versus host disease, we stimulate PBMCs before transferring them into either female or male NSG mice. This method enhances the survival and maintenance of the engrafted cells. Human T cells and B cells that are critical to lupus development can be detected in the peripheral blood and spleen of humanized mice with no sex preference two weeks after engraftment. The model responds well to dexamethasone treatment with reduced proteinuria and decrease of spleen weight, indicating that our model could be used for preclinical studies for SLE. The therapeutic window can be as long as 3 weeks. This model allows for mechanistic studies and testing of potential therapies of SLE directly on human immune system in vivo without putting human life at risk.

Dysbiosis of gut microbiota promotes autoimmune disorders that damage organs outside the intestine. Here we report the role of gut microbiota in the pathogenesis of renal dysfunction in systemic lupus erythematosus. In a classical mouse model of lupus nephritis, MRL/lpr, we found marked depletion of Lactobacillus spp. in the gut microbiota. Increasing Lactobacilli in the gut improved renal function of these mice. Further studies revealed that MRL/lpr mice possessed a “leaky” gut, which was reversed by Lactobacilli. Lactobacillus treatment also decreased mucosal IL-6 and increased mucosal IL-10, thereby providing an anti-inflammatory environment in the gut. In addition, it increased IL-10 and decreased IgG2a in the circulation, the latter a major immune deposit in the kidney of MRL/lpr mice. Inside the kidney, Treg-Th17 balance was skewed towards Treg with Lactobacillus treatment. These effects of Lactobacilli were present in female and castrated male mice, but not in unaltered males, suggesting that beneficial bacteria in the gut attenuate lupus nephritis in a sex hormone-dependent manner.

Little is known on the role of commensal bacteria in lupus. We previously showed that a higher abundance of Lactobacillaceae and a lower abundance of Lachnospiraceae are correlated with improved lupus symptoms in lupus-prone MRL/lpr mice. In the same study, it was noted that Lactobacillaceae (“good” bacteria) was more abundant in the gut of pre-disease lupus mice, while Lachnospiraceae (“bad” bacteria) was relatively more abundant after disease onset. We thus hypothesized that antibiotic use after disease onset might have a greater impact on “bad” than “good” bacteria, thus attenuating the disease. To test this hypothesis, we treated MRL/lpr mice with antibiotics starting from 3 weeks (pre-disease, Abx-3w) or 9 weeks of age (after disease onset, Abx-9w). Consistent with the results obtained from germ-free MRL/lpr mice, Abx-3w did not change disease course or severity. Treatment with Abx-9w, however, was able to significantly reduce spleen and lymph node weight, serum level of anti-dsDNA IgG, proteinuria, and renal pathology. Bacterial profiling analysis revealed that >99% of bacteria were removed by Abx-3w, while 20% bacteria remained with Abx-9w treatment, where Lactobacillales and Enterobacteriales were enriched. Further studies are underway to investigate the immunological mechanisms of how Abx-9w attenuated lupus in these mice. The results of this study will increase our understanding of how environmental triggers, such as antibiotic use, are associated with lupus.