Background/Purpose: SLE is an autoimmune disease that causes progressive multi-organ damage, leading to renal injury, or lupus nephritis (LN), in half of patients. Despite treatment, 20% progress to renal failure within 15 years (1). Recent studies show that about 40% of LN flares are linked to intestinal expansions of the human pathobiont Ruminococcus gnavus (RG), which produces an immunogenic pro-inflammatory cell wall lipoglycan (LG) (2). LN patients with gut dysbiosis may represent a distinct endotype, where increased gut permeability and microbial factors contribute to pathogenesis. In murine studies, we have demonstrated gut colonization of mice with human RG strains (3,4). Notably, in Sle1.Sle2.Sle3 B6 congenic lupus-prone mice, colonization with an LG+ strain accelerated disease progression (4). To investigate pathogenic mechanisms, we here used a different lupus-prone murine model to elucidate the pathways connecting RG-driven platelet activation to worsening renal disease progression.

Methods: Using whole-blood transcriptomics, we recently demonstrated that RG intestinal colonization induced platelet and myeloid cell activation (manuscript submitted). Here, lupus-prone FcgRIb−/− B6 congenic mice were either sham-treated or colonized with RG strains, including isogenic paired strains that differ only in LG production. Colonization was confirmed by fecal qPCR. Splenic megakaryocytes were quantified by CD41+ immunofluorescence. Renal histology was evaluated by H&E.

Results: Colonization with LG+ RG resulted in increased intestinal permeability, as quantified by serum detection of orally administered fluorochrome-labeled dextran (FITC-dextran, Fig. 1B). Increased gut leakiness correlated with prominent lymphoid follicles in the small intestine (Fig. 1C,D). RG colonization with LG-producing strains induced persistent platelet activation (Fig 2C), as well as extramedullary expansions of platelet progenitors (megakaryocytes), in the spleen (Fig 1E & 2A). Renal injury was induced as documented by increased tubulointerstitial lymphoid infiltrates (Fig. 3). To assess the direct pathogenic effects of purified LG, mice were given an intraperitoneal LG injection, which also induced persistent splenic megakaryocytosis that was detected after 6 days (Fig. 1G).

Conclusion: To understand how the RG pathobiont induces systemic platelet activation and neutrophil death extracellular trap release (i.e. NETosis) in a subset of active LN patients, we have here elucidated distinct pathogenic pathways of this newly identified endotype of proliferative LN. In murine models, we have documented that RG strains that produce an immunostimulatory lipoglycan cause the expansion of splenic megakaryocytes and renal disease exacerbation. References1. Anders HJ et al. NatRevDzPrimers 2020; 6(1):72. Azzouz DA et al. ARD 2023; 0:1-133. Silverman GJ et al. Front Immun 2022; Vol 134. Ma L et al. ACR Open 2025;7.5;e70033

Figure 1. Effect of R. gnavus gavage and RG-immunodominant lipoglycan on the intestine and spleen. (A) Mice were orally treated with antibiotics, then subsequently orally gavaged with RG culture or sham (B). Serum FITC-dextran levels were determined pre- and post-oral gavage of sham vs. RG-treated (RG colonized B6) mice. (C) Lymphoid aggregates were observed in sham (left) vs. RG-colonized (right) B6 mice at the terminal ileum. (D) Quantification of total prominent lymphoid aggregates, which were scored in the equivalent total length of the distal small intestine in Swiss rolls. Scoring was based on the number of lymphoid cells per aggregate; +0.5 represents 25-55 lymphocytes/aggregate, +1: 56-149/ aggregate, +2: 150–299/ aggregate, +3:300+ /aggregate, and +1:GC identified. (E,F) Immunofluorescence of splenic megakaryocyte in B6 mice after RG gavage as identified by CD41+. In 3-4 months old, female. (G,H) IF megakaryocyte quantification in the spleens of 5-8 month old lupus-prone, female FcgRIIb-/- mice at six days after a single LG intraperitoneal injection (2ug/g). (E-H) Cell count per high-powered field, in at least three mice per group. *p < 0.05. ***p < 0.01.

Figure 2. Pathogenic R. gnavus strains that produce lipoglycan, but not strains without lipoglycan, drive increases in splenic megakaryocytes. (A) Immunofluorescence of splenic megakaryocyte in FCGRIIb-/- mice as defined by CD41+ after RG gavage with lipoglycan-positive strains (nb92, RG2) versus strains without lipoglycan (nb90). 12 months old, female. (B) Cell count per high-powered field, at least three mice per group.**p < 0.02, ***p < 0.01 (C, D) Platelet activation induced by a single intraperitoneal injection of lipoglycan in FCGRIIb-/- mice was evaluated by flow cytometric monitoring of the percentage of surface P-selectin expressing cells after thrombin stimulation at 8 hours, 2 days (48 hours), and 6 days (144 hours) after administering 1.5 µg/g of lipoglycan. *p < 0.05. (C) shows mean with range.

Figure 3. R. gnavus gut colonization causes increased renal cellular infiltration in lupus-prone mice. (A) Representative kidney sections (H&E) after FcgRIIb-/- colonization with lipoglycan-positive R. gnavus strains (nb92, RG2), and lipoglycan-non-producing isogenic (nb90) strains. (B) Quantification of the renal activity index is scored based on a blinded review for the presence (scored from 0-3) of mononuclear cells in the tubulointerstitium, glomerular leukocyte infiltration, and deposition of hyaline thrombi, closed capillary loops, or early crescent formation/fibrotic ring. *p < 0.05.(C) 40x magnification example glomeruli of RG2 (LG producing strain) colonized FcgRIIB-/- lupus-prone mice, showing hyalinization (left, middle), and mononuclear interstitial cellular infiltrations (right).

« Back to ACR Convergence 2025

ACR Meeting Abstracts - https://acrabstracts.org/abstract/role-of-a-pathogenic-bacterial-factor-produced-by-a-human-gut-pathobiont-in-inducing-platelet-activation-and-thrombo-inflammation/