Animal models of vasculitis.

PURPOSE OF REVIEW: Vasculitis describes a wide spectrum of rare, inflammatory, multisystem disorders. These heterogenous diseases all have inflammation of blood vessels as a central feature. However, they differ in terms of their genetic and environmental risk factors, disease pathogenesis, clinical presentations and treatment strategies. Many animal models of vasculitis exist, each resembling a different human clinical phenotype. This review provides an overview of recently published findings from experimental animal models of vasculitis. RECENT FINDINGS: Several new animal models have been described during the review period. New insights gleaned from existing animal models regarding cause, disease effector mechanisms and novel treatments identified in established animal models are discussed. SUMMARY: Animal models continue to be an important tool for understanding disease pathogenesis, especially in rare and complex diseases such as vasculitis. They also provide an invaluable platform for development and preclinical testing of new treatments.

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

OBJECTIVES: ANCA-associated vasculitis (AAV) is an autoimmune disease characterized 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 (MPO), an autoantigen responsible for AAV, increases with age, anti-MPO 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 months) mice were immunized with whole proteins or peptides from ovalbumin, as a model foreign antigen, or MPO protein or peptides. Mice were subjected to a model of active anti-MPO 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 MPO 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 IFN-γ and IL-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 AAV in older people.

The fragility of significant results underscores the need of larger randomized controlled trials in nephrology.

The Fragility Index is a tool for testing robustness of randomized controlled trial results for dichotomous outcomes. It describes the minimum number of individuals in whom changing an event status would render a statistically significant result nonsignificant. Here we identified all randomized controlled trials in five nephrology and five general journals from 2005-2014. A total of 127 randomized controlled trials reporting at least one dichotomous statistically significant outcome (p less than 0.05) were included and the Fragility Index was calculated. Twenty randomized controlled trials had a Fragility Index of zero and were excluded from further analysis. Linear regression was performed to assess factors associated with Fragility Indexes stratified by primary or secondary outcomes. The median sample size was 134 (range 2211506) with 36 (range 5-2743) total number of events. The median Fragility Index was three (range 1-166), indicating that in half the trials the addition of three events to the treatment with the lowest number of events rendered the result nonsignificant. For primary outcome studies a doubling in total event number and sample size significantly increased the geometric mean Fragility Index by 52% and 42%, respectively. Compared to a reported p value of 0.05 to 0.01, those reporting 0.01 to 0.001 or less than 0.001 had a significant 57% and 472% increase in the median Fragility Index, respectively. Forty-one percent had a Fragility Index less than the total loss to follow-up, indicating a potential to change a trial result had all individuals been accounted for. Thus, our study highlights the need for larger randomized controlled trials with accurate accounting for loss to follow-up to adequately guide evidence-based practice.

De novo thrombotic microangiopathy following simultaneous pancreas and kidney transplantation managed with eculizumab.

Thrombotic microangiopathy (TMA) is a well-recognised complication following transplantation, often due to an underlying genetic predisposition, medications or rejection. The use of eculizumab in these settings has been previously described, but its role still remains to be clarified. A 45-year-old man, with a history of type 1 diabetes mellitus and subsequent end-stage kidney failure, presented for a simultaneous pancreas-kidney transplant. Immunologically, he was well matched with the donor, and he received standard induction immunosuppression including tacrolimus. His early transplant course was complicated by Haemophilus parainfluenzae paronychia and a Pseudomonas aeruginosa catheter-associated urinary tract infection. Within 1 week, he developed thrombotic microangiopathy with significant renal dysfunction and eventual dialysis dependence, without evidence of transplant rejection on biopsy. He was also noted to have antiphospholipid antibodies in moderate titres. The TMA did not resolve despite cessation of tacrolimus, and he was subsequently commenced on eculizumab. The patient achieved a partial remission from TMA, with ongoing biochemical evidence of haemolysis, although now with stable graft function, despite significant damage. His transplanted pancreas remained seemingly unaffected by TMA, and continues to function well. This case describes an unusual presentation of TMA post-transplantation and is the only described case of eculizumab use following pancreas-kidney transplant. It remains unclear in this case what the likely precipitant for TMA was, although it seems to be, at least in part, controlled by ongoing use of eculizumab, presumably by terminal complement inhibition.

Epstein-Barr virus encephalitis in solid organ transplantation.

Epstein-Barr virus (EBV) is typically associated with post transplant lymphoproliferative disease (PTLD) after solid organ and stem cell transplantation. However, it is rarely associated with neurological complications. We report a case of severe encephalitis complicating primary EBV infection six months post renal transplantation, and review the literature on EBV encephalitis in solid organ transplantation in adults. A 55-year-old male presented 6 months post cadaveric renal transplant with headache, fever and confusion. Neuroimaging was unremarkable, but an electroencephalogram was consistent with diffuse encephalopathy. EBV DNA was detected in both cerebrospinal fluid (13,177 copies/ml), and plasma (14,166 copies/ml). Management included reduction of immunosuppression, intravenous ganciclovir and intravenous immunoglobulin, and resulted in a reduction in EBV viral load in both plasma and cerebrospinal fluid. The patient made a full recovery with no long-term neurological deficits and preservation of the graft. This case highlights the importance of knowing donor and recipient EBV serostatus at time of transplant, and closely monitoring EBV DNA when there is a mismatch. Ganciclovir or valganciclovir prophylaxis has also been shown to reduce the incidence of primary EBV infection in renal transplantation in these recipients. Treatment options for EBV infection post-transplant include reduction of immunosuppression, antiviral therapy, IVIg, and monoclonal antibody therapy directed toward infected B lymphocytes.

Animal Models of ANCA Associated Vasculitis.

Anti-neutrophil cytoplasmic antibody (ANCA) associated vasculitis (AAV) is a rare and severe autoimmune multisystemic disease. Its pathogenesis involves multiple arms of the immune system, as well as complex interactions between immune cells and target organs. Experimental animal models of disease can provide the crucial link from human disease to translational research into new therapies. This is particularly true in AAV, due to low disease incidence and substantial disease heterogeneity. Animal models allow for controlled environments in which disease mechanisms can be defined, without the clinical confounders of environmental and lifestyle factors. To date, multiple animal models have been developed, each of which shed light on different disease pathways. Results from animal studies of AAV have played a crucial role in enhancing our understanding of disease mechanisms, and have provided direction toward newer targeted therapies. This review will summarize our understanding of AAV pathogenesis as has been gleaned from currently available animal models, as well as address their strengths and limitations. We will also discuss the potential for current and new animal models to further our understanding of this important condition.

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 (MPO409-428), can induce anti-MPO autoimmunity. The peptide (6PGD391-410) 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 6PGD391-410, or with S. aureus containing a plasmid expressing 6PGD391-410, 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 6PGD391-410 is immunogenic in humans, as healthy human and AAV patient sera contain anti-6PGD and anti-6PGD391-410 antibodies. Therefore, our results support the idea that bacterial plasmids might have a function in autoimmune disease.