Elevated IgA Plasmablast Levels in Subjects at Risk of Developing Rheumatoid Arthritis

Abstract

Objective The disease process in rheumatoid arthritis (RA) starts years before clinical diagnosis, and elevated disease-specific autoantibodies can be detected in this period. Early responses to known or novel autoantigens likely drive the eventual production of pathogenic autoimmunity. Importantly, the presence of disease-specific autoantibodies can identify individuals who are at high-risk for future RA onset but are currently without arthritis. The goal of the current studies is to characterize plasmablasts in these individuals. Methods We investigated the antibody-secreting plasmablasts of a well characterized cohort of individuals at-risk for RA based on serum RA-related autoantibody positivity (Ab+) in comparison to patients with early (<1 yr) seropositive RA and healthy controls. The plasmablast antibody repertoires of at-risk subjects were analyzed using DNA barcode-based methods with paired heavy- and light-chain gene sequencing. Cells were single-cell sorted prior to sequentially adding cell- and plate-specific DNA barcodes, followed by next-generation sequencing. Results Total plasmablast levels were similar in Ab+ individuals (1%) and controls (0.4–1.6%). However, increased frequencies of IgA+ vs. IgG+ plasmablasts were observed in Ab+ individuals (39% IgA+, 37% IgG+ plasmablasts) as compared to other groups (1–9% IgA+, 71–87% IgG+ plasmablasts). Paired antibody sequences from Ab+ subjects revealed cross-isotype clonal families and similar sequence characteristics between the IgA and IgG plasmablast repertoires. Ab+ individuals also demonstrated elevated serum levels of IgA isotype anti-CCP3 antibodies. Conclusion The IgA plasmablast dominance in these Ab+ individuals suggests that a subset of RA-related autoantibodies may arise from mucosal immune responses and be involved in early disease pathogenesis in individuals who are at-risk for developing RA.

Immunopathogenesis of Rheumatoid Arthritis

“…More recent studies have shown signs of local inflammation in bronchial tissues of untreated RA patients (Reynisdottir et al 2016). Using B cell barcoding techniques, the frequency of circulating IgA plasmablasts was found to be elevated in at risk subjects without RA who are ACPA positive providing further evidence for a mucosal origin for at least a proportion of the autoimmunity detected in RA (Kinslow J et al 2016). …”

Genetic and environmental risk factors for rheumatoid arthritis

“…There is also a growing knowledge of how microbes influence human immunity both at mucosal surfaces and systemically. With relevance to RA pathogenesis, there is an emerging understanding of mucosal-associated immunoglobulin A (IgA)-related autoimmunity as a possible early factor in disease development that is based on autoantibody isotype studies as well as plasmablast studies (133, 134). …”

“…antibodies to carbamylated proteins and heat-shock proteins (157–159)), these aspects need to be included in models of disease development. Other processes that need to be explored include the role of neutrophil extracelluar traps (NETs) and inflammasomes in mucosal and systemic autoimmunity (160, 161), and emerging technologies that can elucidate single cell phenotypes (including IgA production) mucosally or systemically (134). Finally, it will be critically important to integrate all of these factors to understand how mucosal processes relate to other factors associated with RA such as genetics, familial factors, and sex, as well as environmental factors such as exposure to tobacco smoke, or dietary factors.…”

Leveraging blood and tissue CD4+ T cell heterogeneity at the single cell level to identify mechanisms of disease in rheumatoid arthritis

“…Building a reference map of the human immune system is a difficult and complicated task; however, the dendritic cell atlas or the work of Wong et al characterizing T cells across tissues provide examples of the power of this approach [57••, 104•]. Incorporating data on from multiple assays to define lymphocyte profiles will be essential for understanding their functional impact, as shown by multiple studies that utilize repertoire sequences or expression data in combination with single cell cytometry to identify disease-relevant populations [71••,105•,106,107]. The development of new peptide-MHC multimeric complexes supports the detection and isolation of antigen-specific lymphocytes at much lower frequencies [108] than was previously feasible.…”