Ectopic Lymphoid Structures Support Ongoing Production of Class-Switched Autoantibodies in Rheumatoid Synovium

Abstract

BackgroundFollicular structures resembling germinal centres (GCs) that are characterized by follicular dendritic cell (FDC) networks have long been recognized in chronically inflamed tissues in autoimmune diseases, including the synovium of rheumatoid arthritis (RA). However, it is debated whether these ectopic structures promote autoimmunity and chronic inflammation driving the production of pathogenic autoantibodies. Anti-citrullinated protein/peptide antibodies (ACPA) are highly specific markers of RA, predict a poor prognosis, and have been suggested to be pathogenic. Therefore, the main study objectives were to determine whether ectopic lymphoid structures in RA synovium: (i) express activation-induced cytidine deaminase (AID), the enzyme required for somatic hypermutation and class-switch recombination (CSR) of Ig genes; (ii) support ongoing CSR and ACPA production; and (iii) remain functional in a RA/severe combined immunodeficiency (SCID) chimera model devoid of new immune cell influx into the synovium.Methods and FindingsUsing immunohistochemistry (IHC) and quantitative Taqman real-time PCR (QT-PCR) in synovial tissue from 55 patients with RA, we demonstrated that FDC+ structures invariably expressed AID with a distribution resembling secondary lymphoid organs. Further, AID+/CD21+ follicular structures were surrounded by ACPA+/CD138+ plasma cells, as demonstrated by immune reactivity to citrullinated fibrinogen. Moreover, we identified a novel subset of synovial AID+/CD20+ B cells outside GCs resembling interfollicular large B cells. In order to gain direct functional evidence that AID+ structures support CSR and in situ manufacturing of class-switched ACPA, 34 SCID mice were transplanted with RA synovium and humanely killed at 4 wk for harvesting of transplants and sera. Persistent expression of AID and Iγ-Cμ circular transcripts (identifying ongoing IgM-IgG class-switching) was observed in synovial grafts expressing FDCs/CD21L. Furthermore, synovial mRNA levels of AID were closely associated with circulating human IgG ACPA in mouse sera. Finally, the survival and proliferation of functional B cell niches was associated with persistent overexpression of genes regulating ectopic lymphoneogenesis.ConclusionsOur demonstration that FDC+ follicular units invariably express AID and are surrounded by ACPA-producing plasma cells provides strong evidence that ectopic lymphoid structures in the RA synovium are functional and support autoantibody production. This concept is further confirmed by evidence of sustained AID expression, B cell proliferation, ongoing CSR, and production of human IgG ACPA from GC+ synovial tissue transplanted into SCID mice, independently of new B cell influx from the systemic circulation. These data identify AID as a potential therapeutic target in RA and suggest that survival of functional synovial B cell niches may profoundly influence chronic inflammation, autoimmunity, and response to B cell–depleting therapies.

Identification of New Pathogenic Players in Lupus: Autoantibody-Secreting Cells Are Present in Nephritic Kidneys of (NZBxNZW)F1 Mice

“…lupus (A, B). Centered on nucleosome immunity, these mechanisms involve either direct binding of nucleosome/dsDNA autoantibodies to inherent glomerular constituents, such as membrane structures or a-actinin or nucleosome-mediated binding of nucleosome/dsDNA autoantibodies to heparan sulfate, collagen IV, laminin, or other constituents of the GBM (10,14,16,(43)(44)(45)(46)(47)(48). Based on the present findings in NZB/W mice, an additional player has to be included in this scheme (C).…”

Immune infiltration in human tumors: a prognostic factor that should not be ignored

“…In this situation, their increase in size and number correlates with disease severity and local production of autoantibodies with an oligoclonal repertoire and hypersomatic mutations (Gause et al, 1995;Kotlan et al, 2003;RangelMoreno et al, 2006;Carragher et al, 2008;Humby et al, 2009). On the contrary, the development of tertiary lymphoid structures, which occurs in nonlymphoid organs in several infectious diseases, may be beneficial and help to resolve the infection.…”

Ectopic lymphoid follicles: inducible centres for generating antigen‐specific immune responses within tissues

“…Although the mechanisms contributing the development of this form of pathology are largely unclear, ELFs in rheumatoid arthritis are associated with heightened synovial expression of CXCL13, CCL21, CCL19 and CXCL12, and cytokines LT α 1 β 2 and IL‐7 21, 44, 114, 115. Importantly, these structures correlate with disease severity and are associated with local T‐cell priming and autoantibody production 43, 116, 117, 118. Plasma cells in rheumatoid synovitis produce autoantibodies against citrullinated protein/peptides (ACPA/anti‐CCP) 116.…”

“…Importantly, these structures correlate with disease severity and are associated with local T‐cell priming and autoantibody production 43, 116, 117, 118. Plasma cells in rheumatoid synovitis produce autoantibodies against citrullinated protein/peptides (ACPA/anti‐CCP) 116. Using an elegant human rheumatoid arthritis–severe combined immunodeficient (HuRA–SCID) mouse chimera model, Humby et al .…”