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.

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.

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.