Systemic lupus erythematosus and the gut microbiome: To look forward is to look within - A systematic review and narrative synthesis.

Background: Systemic lupus erythematosus (SLE) is a heterogeneous autoimmune disease shaped by complex interactions involving genetic and environmental factors. Among these, the gut microbiome is emerging as potentially modulating immune responses and influencing disease susceptibility, progression, and activity.

Objectives: To synthesize current evidence on gut microbiome changes in adult SLE patients, framed along the clinical pathway - from diagnosis to treatment - to help bridge bench and bedside for microbiome-informed SLE care and research.

Methods: A systematic search identified primary research studies examining gut microbiota in adult SLE patients. Studies were reviewed in a stepwise manner by independent investigators. Findings were synthesized narratively, emphasizing human data.

Results: SLE patients exhibit gut microbiome dysbiosis, with reduced microbial richness and altered bacterial taxa. A lower Firmicutes/Bacteroidetes ratio is frequently observed. Enrichment of specific taxa, such as Enterococcus, Lactobacillus, and Ruminococcus gnavus, is reported. Dysbiosis correlates with increased gut permeability, immune activation, and autoreactivity. Clinical associations include disease activity, flares, nephritis, and other manifestations. SLE treatments, such as hydroxychloroquine and corticosteroids, influence the microbiome. Emerging interventions such as dietary modulation and fecal microbiota transplantation show promise in early studies. However, considerable heterogeneity exists across studies in terms of patient characteristics, methodology, and taxa-level findings.

Conclusions: The gut microbiome has multifaceted associations with SLE pathogenesis, disease activity, and therapeutic response. Translation will require standardized methods, functional validation, longitudinal follow-up, and clinical integration. While uncertainties remain, the gut microbiome is increasingly relevant, and clinicians caring for patients with SLE should be aware of its emerging implications.