Pauci-immune RPGN?

[Nice Marmot]

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Why is rapidly progressive glomerulonephritis (RPGN) caused by Wegner's or Microscopic polyangiitis considered "pauci-immune"? I get that in Goodpasture's you have lots of antibody against the glomerular basement membrane, so when you do immunofluorescence (IF), it lights up (excluding it from the "pauci-immune" category).

But don't Wegner's and Microscopic polyangiitis, by definition, also display positive IF against c-ANCA and p-ANCA, respectively? Isn't that what ANCA means (anti-neutrophil cytoplasmic antibody)? So why is considered "pauci-immune" if you can still get a positive IF signal by staining for ANCA in a renal biopsy?

 

[Entadus]

Pauci-immune refers to a lack of immune COMPLEXES ... so you would have antibody against ANCA but would not see any immune complex deposition in blood vessels.... for example Wegener's has PR3-ANCA (C-ANCA) antibodies but the main histologic features would be granulomas......

I hope this helps this is just my naive understanding

 

[newyorkcitymed]

Pauci-immune refers to a lack of immune COMPLEXES ... so you would have antibody against ANCA but would not see any immune complex deposition in blood vessels.... for example Wegener's has PR3-ANCA (C-ANCA) antibodies but the main histologic features would be granulomas......

I hope this helps this is just my naive understanding

I don't think that's it. Because Goodpasture doesn't have immune complexes either - it's a type II hypersensitivity reaction, i.e. antibodies directly to the basement membrane, yet it is considered to have positive (linear) immunofluorescence.

I believe "pauci-immune" just means "doesn't light up very much on immunofluorescence." When you do IF in someone with glomerulonephritis, these are the options:

1. Linear (Goodpasture)
2. Mesangial (IgA nephropathy)
3. Granular (could be post-strep GN, lupus GN, or membranoproliferative GN)
4. Pauci-immune (which is Wegener's or MPA)
5. And then there's Alport syndrome, which have completely negative IF, since it is not an immune condition