T cell mediated autoimmune glomerular disease in mice

Ageing enhances cellular immunity to myeloperoxidase and experimental anti-myeloperoxidase glomerulonephritis

OBJECTIVES

Anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis is an autoimmune disease characterised by small blood vessel inflammation, commonly affecting the kidneys and respiratory tract. It is unclear why the incidence of this condition increases with age. Previous studies in a passive antibody transfer system in aged mice have implicated innate effectors. To test the hypothesis that autoimmunity to myeloperoxidase, an autoantigen responsible for ANCA-associated vasculitis, increases with age, anti-myeloperoxidase autoimmunity was studied in murine models of active autoimmunity and disease induced by cellular immunity.

METHODS

Young (8 weeks) and aged (either 15 or 22 month) mice were immunised with whole proteins or peptides from ovalbumin, as a model foreign antigen, or myeloperoxidase protein or peptides. Mice were subjected to a model of active anti-myeloperoxidase glomerulonephritis. Cellular and humoral immune responses and tissue inflammation were assessed.

RESULTS

While cellular immunity to ovalbumin was diminished in aged mice, cellular autoimmunity to myeloperoxidase and its immunodominant CD4+ and CD8+ T cell epitopes was increased after immunization with either MPO peptides or whole MPO protein, assessed by peptide and antigen specific production of the pro-inflammatory cytokines interferon-γ and interleukin-17A. MPO-ANCA titres were not increased in aged mice compared with young mice. In experimental anti-MPO glomerulonephritis, cell mediated injury was increased, likely due to CD4+ and CD8+ T cells, innate immunity and the increased vulnerability of aged kidneys.

CONCLUSION

Heightened cellular immunity to MPO develops with ageing in mice and may contribute to the increased incidence and severity of ANCA-associated vasculitis in older people.

Characterisation of an enhanced preclinical model of experimental MPO-ANCA autoimmune vasculitis

Experimental autoimmune vasculitis (EAV) is a model of antineutrophil cytoplasm antibody (ANCA)-associated vasculitis (AAV) induced by immunisation of susceptible rat strains with myeloperoxidase (MPO). Animals develop circulating MPO-ANCA, pulmonary haemorrhage, and glomerulonephritis, although renal injury is mild and recovers spontaneously without treatment. In this study we aimed to augment the severity of glomerulonephritis. Following induction of EAV on day 0, a sub-nephritogenic dose of nephrotoxic serum (NTS) containing heterologous antibodies to glomerular basement membrane was administered on day 14. This resulted in a significant increase in disease severity at day 28 compared to MPO immunisation alone - with more urinary abnormalities, infiltrating glomerular leucocytes, and crescent formation that progressed to glomerular and tubulointerstitial scarring by day 56, recapitulating important features of human disease. Importantly, the glomerulonephritis remained pauci-immune, and was strictly dependent on the presence of autoimmunity to MPO, as there was no evidence of renal disease following administration of sub-nephritogenic NTS alone or after immunisation with a control protein in place of MPO. Detailed phenotyping of glomerular leucocytes identified an early infiltrate of non-classical monocytes following NTS administration that, in the presence of autoimmunity to MPO, may initiate the subsequent influx of classical monocytes which augment glomerular injury. We also showed that this model can be used to test novel therapeutics by using a small molecule kinase inhibitor (fostamatinib) that rapidly attenuated both glomerular and pulmonary injury over a 4-day treatment period. We believe that this enhanced model of MPO-AAV will prove useful for the study of glomerular leucocyte behaviour and novel therapeutics in AAV in the future. © 2021 The Authors. The Journal of Pathology published by John Wiley & Sons, Ltd. on behalf of The Pathological Society of Great Britain and Ireland.

A plasmid-encoded peptide from Staphylococcus aureus induces anti-myeloperoxidase nephritogenic autoimmunity

Autoreactivity to myeloperoxidase (MPO) causes anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV), with rapidly progressive glomerulonephritis. Here, we show that a Staphylococcus aureus peptide, homologous to an immunodominant MPO T-cell epitope (MPO_409–428), can induce anti-MPO autoimmunity. The peptide (6PGD_391–410) is part of a plasmid-encoded 6-phosphogluconate dehydrogenase found in some S. aureus strains. It induces anti-MPO T-cell autoimmunity and MPO-ANCA in mice, whereas related sequences do not. Mice immunized with 6PGD_391–410, or with S. aureus containing a plasmid expressing 6PGD_391–410, develop glomerulonephritis when MPO is deposited in glomeruli. The peptide induces anti-MPO autoreactivity in the context of three MHC class II allomorphs. Furthermore, we show that 6PGD_391–410 is immunogenic in humans, as healthy human and AAV patient sera contain anti-6PGD and anti-6PGD_391–410 antibodies. Therefore, our results support the idea that bacterial plasmids might have a function in autoimmune disease.

Autoreactivity to myeloperoxidase (MPO) causes autoimmune vasculitis and severe glomerulonephritis. Here, Ooi et al. show that a Staphylococcus aureus plasmid encodes a peptide that is homologous to an immunodominant MPO epitope and induces anti-MPO autoimmunity and glomerulonephritis in mice.

Emerging immunotherapies for autoimmune kidney disease

Autoimmunity is a leading cause of chronic kidney disease and loss of native and transplanted kidneys. Conventional immunosuppressive therapies can be effective but are non-specific, noncurative, and risk serious side effects such as life-threatening infection and cancer. Novel therapies and targeted interventions are urgently needed. In this brief review we explore diverse strategies currently in development and under consideration to interrupt underlying disease mechanisms in immune-mediated renal injury. Because autoantibodies are prominent in diagnosis and pathogenesis in multiple human glomerulopathies, we highlight several promising therapies that interfere with functions of early mediators (IgG and complement) of the effector arm and with an epicenter (the germinal center) for induction of humoral immunity.

ANCA-Associated Vasculitis: Pathogenesis, Models, and Preclinical Testing

Our understanding of antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis has developed greatly since the discovery of ANCA, directed against neutrophil components, in 1982. Observations in human disease, and increasingly sophisticated studies in vitro and in rodent models in vivo, have allowed a nuanced understanding of many aspects of the immunopathogenesis of disease, including the significance of ANCA as a diagnostic and monitoring tool as well as a mediator of microvascular injury. The mechanisms of leukocyte recruitment and tissue injury, and the role of T cells increasingly are understood. Unexpected findings, such as the role of complement, also have been uncovered through experimental studies and human observations. This review focusses on the pathogenesis of ANCA-associated vasculitis, highlighting the challenges in finding new, less-toxic treatments and potential therapeutic targets in this disease. The current suite of rodent models is reviewed, and future directions in the study of this complex and fascinating disease are suggested.

Pathogenic Role for γδ T Cells in Autoimmune Anti-Myeloperoxidase Glomerulonephritis

Myeloperoxidase (MPO) anti-neutrophil cytoplasmic Ab (ANCA)-associated vasculitis results from autoimmunity to MPO. IL-17A plays a critical role in generating this form of autoimmune injury but its cell of origin is uncertain. We addressed the hypothesis that IL-17A-producing γδ T cells are a nonredundant requisite in the development of MPO autoimmunity and glomerulonephritis (GN). We studied MPO-ANCA GN in wild type, αβ, or γδ T cell-deficient (C57BL/6, βTCR^-/- , and δTCR^-/- respectively) mice. Both T cell populations played important roles in the generation of autoimmunity to MPO and GN. Humoral autoimmunity was dependent on intact αβ T cells but was unaffected by γδ T cell deletion. Following MPO immunization, activated γδ T cells migrate to draining lymph nodes. Studies in δTCR^-/- and transfer of γδ T cells to δTCR^-/- mice show that γδ T cells facilitate the generation of anti-MPO autoimmunity and GN. δTCR^-/- mice that received IL-17A^-/- γδ T cells demonstrate that the development of anti-MPO autoimmunity and GN are dependent on γδ T cell IL-17A production. Finally, transfer of anti-MPO CD4⁺ T cell clones to naive δTCR^-/- and wild type mice with planted glomerular MPO shows that γδ T cells are also necessary for recruitment of anti-MPO αβ CD4⁺ effector T cells. This study demonstrates that IL-17A produced by γδ T cells plays a critical role in the pathogenesis of MPO-ANCA GN by promoting the development of MPO-specific αβ T cells.

Regulatory T cells in immune-mediated renal disease

Regulatory T cells (Tregs) are CD4+ T cells that can suppress immune responses by effector T cells, B cells and innate immune cells. This review discusses the role that Tregs play in murine models of immune-mediated renal diseases and acute kidney injury and in human autoimmune kidney disease (such as systemic lupus erythematosus, anti-glomerular basement membrane disease, anti-neutrophil cytoplasmic antibody-associated vasculitis). Current research suggests that Tregs may be reduced in number and/or have impaired regulatory function in these diseases. Tregs possess several mechanisms by which they can limit renal and systemic inflammatory immune responses. Potential therapeutic applications involving Tregs include in vivo induction of Tregs or inducing Tregs from naïve CD4+ T cells or expanding natural Tregs ex vivo, to use as a cellular therapy. At present, the optimal method of generating a phenotypically stable pool of Tregs with long-lasting suppressive effects is not established, but human studies in renal transplantation are underway exploring the therapeutic potential of Tregs as a cellular therapy, and if successful may have a role as a novel therapy in immune-mediated renal diseases.

What is myeloperoxidase doing in ANCA-associated glomerulonephritis?

O'Sullivan et al. describe glomerular localization of myeloperoxidase (MPO) in anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) and correlate the amount of deposition with severity of injury. MPO is the antigen against which anti-MPO ANCAs are directed, the antigen to which pathogenic T cells that can induce antibody-independent AAV are directed, and MPO can induce glomerular injury directly by interacting with H2O2 and a halide to halogenate glomerular structures. All three of these roles are likely involved in human disease.

Biologics for the treatment of autoimmune renal diseases

Biological therapeutics (biologics) that target autoimmune responses and inflammatory injury pathways have a marked beneficial impact on the management of many chronic diseases, including rheumatoid arthritis, psoriasis, inflammatory bowel disease, and ankylosing spondylitis. Accumulating data suggest that a growing number of renal diseases result from autoimmune injury - including lupus nephritis, IgA nephropathy, anti-neutrophil cytoplasmic antibody-associated glomerulonephritis, autoimmune (formerly idiopathic) membranous nephropathy, anti-glomerular basement membrane glomerulonephritis, and C3 nephropathy - and one can speculate that biologics might also be applicable to these diseases. As many autoimmune renal diseases are relatively uncommon, with long natural histories and diverse outcomes, clinical trials that aim to validate potentially useful biologics are difficult to design and/or perform. Some excellent consortia are undertaking cohort studies and clinical trials, but more multicentre international collaborations are needed to advance the introduction of new biologics to patients with autoimmune renal disorders. This Review discusses the key molecules that direct injurious inflammation and the biologics that are available to modulate them. The opportunities and challenges for the introduction of relevant biologics into treatment protocols for autoimmune renal diseases are also discussed.

Galectin-3 in autoimmunity and autoimmune diseases

Galectin-3 (gal-3) is a β-galactoside-binding lectin, which regulates cell-cell and extracellular interactions during self/non-self-antigen recognition and cellular activation, proliferation, differentiation, migration and apoptosis. It plays a significant role in cellular and tissue pathophysiology by organizing niches that drive inflammation and immune responses. Gal-3 has some therapeutic potential in several diseases, including chronic inflammatory disorders, cancer and autoimmune diseases. Gal-3 exerts a broad spectrum of functions which differs according to its intra- or extracellular localization. Recombinant gal-3 strategy has been used to identify potential mode of action of gal-3; however, exogenous gal-3 may not reproduce the functions of the endogenous gal-3. Notably, gal-3 induces monocyte-macrophage differentiation, interferes with dendritic cell fate decision, regulates apoptosis on T lymphocytes and inhibits B-lymphocyte differentiation into immunoglobulin secreting plasma cells. Considering the influence of these cell populations in the pathogenesis of several autoimmune diseases, gal-3 seems to play a role in development of autoimmunity. Gal-3 has been suggested as a potential therapeutic agent in patients affected with some autoimmune disorders. However, the precise role of gal-3 in driving the inflammatory process in autoimmune or immune-mediated disorders remains elusive. Here, we reviewed the involvement of gal-3 in cellular and tissue events during autoimmune and immune-mediated inflammatory diseases.