Background/Purpose: Infectious triggers have been implicated in transient antiphospholipid antibody production in both mice and humans. The cause of persistent anti-β₂-glycoprotein I (β₂GPI) antibody production in the lupus-related antiphospholipid syndrome (APS) is unknown. We hypothesize that pathogenic antiphospholipid antibodies in the spontaneous (NZWxBXSB)F₁ model of APS/SLE are induced and sustained by the gut microbiota that chronically colonizes its host. We therefore generated commensal-ablated animals in order to test if depletion of the microbiota with broad-spectrum antibiotics leads to attenuation of the APS phenotype characterized by multiple non-atherogenic, immune-mediated myocardial infarctions culminating in sudden deaths. 

Methods: Broad-spectrum antibiotic- and control water-treated (NZWxBXSB)F₁ hybrid males were followed until death from autoimmunity. DNA was isolated from fecal pellets (MoBio) and tested for eubacterial load by 16S ribosomal DNA real-time PCR (Bio-Rad). Urine and sera were collected longitudinally and analysed for proteinuria from lupus-related glomerulonephritis and anti-β₂-GPI titers by ELISA (Alpha Diagnostic), respectively. Hematoxylin and eosin-stained slides were prepared from myocardial tissues. Kaplan-Meier survival curves were generated comparing antibiotic- and control water-treated mice.

Results: 16S ribosomal DNA load was profoundly suppressed after treatment with a cocktail of vancomycin, metronidazole, neomycin and ampicillin that was initiated at 6 wks of age. Antibiotic-treated mice had significantly lower titers of anti-β₂GPI antibodies at 4 months of age (p=0.014) and were protected from APS-related deaths (p=0.005). Ceca were markedly enlarged on necropsy as typical also for germ-free animals. Surprisingly, SLE-related proteinuria, known to be driven by an endogenous retroviral protein, was also suppressed in antibiotic-treated mice compared to controls (n=7-8 mice; p=0.026).

Conclusion: Depletion of the gut microbiota with a regimen that approximates a germ-free state in the gastrointestinal tract leads to lower anti-β₂GPI titers and protection from APS-induced myocardial infarctions. These results suggest that gut commensals are fundamentally involved in the pathogenesis of APS. Intriguingly, endogenous retroviral-driven proteinuria secondary to lupus nephritis in the (NZWxBXSB)F₁ hybrid was also suppressed by this regimen, pointing towards a possible interaction between the gut microbiota and retroviruses in systemic autoimmunity. These findings support an unexpected role of commensals in both APS and SLE. Future work is aimed at identifying the causal triggers within the gut microbiome and dissecting the immunologic mechanisms behind the protective effects in this model.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/depletion-of-the-gut-microbiota-prevents-%ce%b22-glycoprotein-i-antibody-production-and-mortality-in-a-model-of-antiphospholipid-syndrome/