Persistent Microbial Peptidoglycan Drives Post-Infectious Autoimmunity in Lyme Disease 2265902

Introduction Persistent symptoms after infection remain a major clinical challenge, yet their immunopathogenesis is poorly understood. Post-Treatment Lyme Disease (PTLD) affects over one million individuals in the United States and is characterized by fatigue, pain, and cognitive dysfunction despite antibiotic clearance of Borrelia burgdorferi. We hypothesized that peptidoglycan–bacterial cell wall remnants that can persist in the host after antibiotic treatment–sustain inflammation and trigger autoimmune-like responses. Methods Peripheral immune cells from PTLD patients and healthy controls fro two clinical cohorts were profiled using single-cell RNA-sequencing analysis. To determine causality, monocytes and human spleen organoids from healthy donors were stimulated with peptidoglycan from Borrelia burgdorferi (PGBb) or from other autoimmune-associated bacterial species. Cellular activation, cytokine secretion, and autoreactive B-cell responses were assessed by flow cytometry, ELISA, and gene expression analysis. Results PTLD patients exhibited an expanded hyperinflammatory monocyte subset expressing autoimmune-associated transcriptional and metabolic programs, along with other immune features characteristic of classical autoimmune diseases. Stimulation of healthy monocytes with PGBb recapitulated these features and induced a distinct proinflammatory cytokine profile. In human spleen organoids, PGBb activated autoreactive B cells and triggered gene expression programs linked to autoimmunity across multiple immune subsets. Peptidoglycans from bacteria associated with rheumatoid arthritis also elicited proinflammatory responses, revealing a conserved yet context-specific mechanism of peptidoglycan-driven autoimmunity. Conclusion Persistent peptidoglycans drive chronic inflammation and may promote autoimmunity in PTLD and related diseases, shaped by species-specific microbial contexts. This work also establishes human spleen organoids as a robust platform for studying autoimmune mechanisms following infection. Funding Source NIH, HHMI, Bill and Melinda Gates Foundation Topic Categories Immune Mechanisms of Human Disease (HUM)