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.

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Data
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Life sciences study design
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Sample size
In previous work in defining immuodominant MPO T cell epitopes a sample size of n=4-6 per group has been sufficient to determine bioloigcla relevance. This approach was also used in the current studies.
Data exclusions No data were excluded from experiments.

Replication
The majority of studies within the work were replicated, as indicated in the manuscript. Some studies were interdependent. As an example. the results of the studies using whole S. aureus are concordant and reinforce each other -they tested the same hypothesis using the same model but in a different manner.
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Blinding
Histological assessment was performed in a blinded fashion on coded slides.
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The study did not involve wild animals.

Field-collected samples
The study did not involve samples collected from the field.

Human research participants
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Sample preparation
To determine the in vivo expansion of MPO specific cells, mice were first immunized with 10 ug of peptide emulsified in FCA subcutaneously base of tail, then, 7 days later, the inguinal, axillary, brachial, cervical, mesenteric, and periaortic lymph nodes and spleen were harvested . Single cell suspensions were made by mechanically pushing lymph nodes and spleen through a 70um mesh.