The mucosal origins hypothesis of rheumatoid arthritis (RA) proposes a central role for mucosal immune responses in the initiation or perpetuation of the systemic autoimmunity that occurs with disease. However, the connection between the mucosa and systemic autoimmunity in RA remains unclear. Using dual immunoglobulin A (IgA) and IgG family plasmablast–derived monoclonal autoantibodies obtained from peripheral blood of individuals at risk for RA, we identified cross-reactivity between RA-relevant autoantigens and bacterial taxa in the closely related families Lachnospiraceae and Ruminococcaceae . After generating bacterial isolates within the Lachnospiraceae/Ruminococcaceae genus Subdoligranulum from the feces of an individual, we confirmed monoclonal antibody binding and CD4 ⁺ T cell activation in individuals with RA compared to control individuals. In addition, when Subdoligranulum isolate 7 but not isolate 1 colonized germ-free mice, it stimulated T _H 17 cell expansion, serum RA–relevant IgG autoantibodies, and joint swelling reminiscent of early RA, with histopathology characterized by antibody deposition and complement activation. Systemic immune responses were likely due to mucosal invasion along with the generation of colon-isolated lymphoid follicles driving increased fecal and serum IgA by isolate 7, because B and CD4 ⁺ T cell depletion not only halted intestinal immune responses but also eliminated detectable clinical disease. In aggregate, these findings demonstrate a mechanism of RA pathogenesis through which a specific intestinal strain of bacteria can drive systemic autoantibody generation and joint-centered antibody deposition and immune activation.

Background Cow's milk intake has been inconsistently associated with islet autoimmunity (IA) and type 1 diabetes (T1D) development. Genetic and environmental factors may modify the effect of cow's milk on IA and T1D risk. Methods The Diabetes Autoimmunity Study in the Young (DAISY) follows children at increased T1D risk of IA (presence of autoantibodies to insulin, GAD65, or IA‐2 twice in succession) and T1D development. We examined 1835 DAISY children with data on cow's milk intake: 143 developed IA, 40 subsequently developed T1D. Cow's milk protein and lactose intake were calculated from prospectively collected parent‐ and self‐reported food frequency questionnaires (FFQ). High risk HLA‐DR genotype: HLA‐DR3/4,DQB1*0302; low/moderate risk: all other genotypes. We examined interactions between cow's milk intake, age at cow's milk introduction, and HLA‐DR genotype in IA and T1D development. Interaction models contained the base terms (e.g., cow's milk protein and HLA‐DR genotype) and an interaction term (e.g., cow's milk protein*HLA‐DR genotype). Results In survival models adjusted for total calories, FFQ type, T1D family history, and ethnicity, greater cow's milk protein intake was associated with increased IA risk in children with low/moderate risk HLA‐DR genotypes [hazard ratio (HR): 1.41, 95% confidence interval (CI): 1.08–1.84], but not in children with high risk HLA‐DR genotypes. Cow's milk protein intake was associated with progression to T1D (HR: 1.59, CI: 1.13–2.25) in children with IA. Conclusions Greater cow's milk intake may increase risk of IA and progression to T1D. Early in the T1D disease process, cow's milk intake may be more influential in children with low/moderate genetic T1D risk.

Rheumatoid arthritis (RA) is a systemic autoimmune disease currently with no universally highly effective prevention strategies. Identifying pathogenic immune phenotypes in at-risk populations prior to clinical onset is crucial to establishing effective prevention strategies. Here, we applied multimodal single-cell technologies (mass cytometry and CITE-Seq) to characterize the immunophenotypes in blood from at-risk individuals (ARIs) identified through the presence of serum antibodies against citrullinated protein antigens (ACPAs) and/or first-degree relative (FDR) status, as compared with patients with established RA and people in a healthy control group. We identified significant cell expansions in ARIs compared with controls, including CCR2 ⁺ CD4 ⁺ T cells, T peripheral helper (Tph) cells, type 1 T helper cells, and CXCR5 ⁺ CD8 ⁺ T cells. We also found that CD15 ⁺ classical monocytes were specifically expanded in ACPA-negative FDRs, and an activated PAX5 ^lo naive B cell population was expanded in ACPA-positive FDRs. Further, we uncovered the molecular phenotype of the CCR2 ⁺ CD4 ⁺ T cells, expressing high levels of Th17- and Th22-related signature transcripts including CCR6 , IL23R , KLRB1 , CD96 , and IL22 . Our integrated study provides a promising approach to identify targets to improve prevention strategy development for RA.

Rheumatoid arthritis (RA) is preceded by an at-risk stage of disease that can be marked by the presence of anticitrullinated protein antibodies (ACPAs) but the absence of clinically apparent synovitis (clinical RA). Preemptive intervention in at-risk individuals could prevent or delay future tissue damage; however, the immunobiology of this stage is unclear. Using integrative multiomics, we longitudinally profiled at-risk individuals, where one-third of participants developed clinical RA on study. We found evidence of systemic inflammation and signatures of activation in naïve T and B cells of at-risk individuals. During progression to clinical RA, proinflammatory skewing of atypical B cells and expansion of memory CD4 T cells with signatures of activation and B cell help were present without elevations in circulating ACPA titers. Epigenetic changes in naïve CD4 T cells suggested a predisposition to differentiate into effector cells capable of B cell help. These findings characterize pathogenesis of the ACPA ⁺ at-risk stage and support the concept that the disease begins much earlier than clinical RA. Additionally, an extensive immune resource of the at-risk stage and progression to clinical RA with interactive tools was developed to enable further investigation.

Rheumatoid arthritis (RA) is an autoimmune disease characterized by synovial hyperplasia and inflammation. The finding of autoantibodies in seropositive RA suggests that complement system activation might play a pathophysiologic role due to the local presence of immune complexes in the joints. Our first objective was to explore the Pathobiology of Early Arthritis Cohort (PEAC) mRNA sequencing data for correlations between clinical disease severity as measured by DAS28-ESR (disease activity score in 28 joints for erythrocyte sedimentation rate) and complement system gene expression, both in the synovium and in blood. Our second objective was to determine the biodistribution using multiplex immunohistochemical staining of specific complement activation proteins and inhibitors from subjects in the Accelerating Medicines Partnership (AMP) RA/SLE study. In the PEAC study, there were significant positive correlations between specific complement gene mRNA expression levels in the synovium and DAS28-ESR for the following complement genes: C2, FCN1, FCN3, CFB, CFP, C3AR1, C5AR1, and CR1. Additionally, there were significant negative correlations between DAS28-ESR and Colec12, C5, C6, MASP-1, CFH, and MCP. In the synovium there were also significant positive correlations between DAS28-ESR and FcγR1A, FcγR1B, FcγR2A, and FcγR3A. Notably, CFHR4 synovial expression was positively correlated following treatment with the DAS28-ESR at 6 mo, suggesting a role in worse therapeutic responses. The inverse correlation of C5 RNA expression in the synovium may underlie the failure of significant benefit from C5/C5aR inhibitors in clinical trials performed in patients with RA. Multiplex immunohistochemical analyses of early RA synovium reveal significant evidence of regional alterations of activation and inhibitory factors that likely promote local complement activation.