ANCA

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The presence of serum auto-antibodies targeting components of the neutrophil cytoplasm. The result given depends on the method of assay. An ELISA (or similar test) will give a quantitative value, i.e. a titre, signifying the dilution at which the test is still positive. In addition, the distribution of the antibodies can be examined using immunofluorescence with which anti-neutrophil cytoplasm antibody activity falls into 2 patterns:

  1. Anti-neutrophil cytoplasmic antibodies with cytoplasmic staining (c-ANCA) is a blood test used when considering the possibility of vasculitic disease, especially if Wegener's granulomatosis is in the differential diagnosis.
  2. The other main type of staining is perinuclear, so is called p-ANCA. This pattern is associated with antibodies to myeloperoxidase and is commonly seen in polyarteritis nodosa, microscopic polyangiitis, Churg-Strauss syndrome and primary sclerosing cholangitis.

Further work has identified the targets of c-ANCA and p-ANCA. c-ANCA is associated with antibodies against neutrophil granulocyte proteinase-3 and is referred more specifically as PR3-ANCA. p-ANCA is associated with myeloperoxidase and is designated (MPO-ANCA). A further antigen, lysosome membrane protein-2 (LAMP-2), represents a further antigen target and may be implicated in certain forms of glomerulonephritis.[1] An epitope on LAMP-2 shares homology with the bacterial adhesin FimH raising the possibility that antibodies against bacterial antigens may cross-react self-proteins resulting in auto-immune disease.[2] Similarly, PR3-ANCA is thought to arise through cross-reactivity of antibodies produced against Staphylococcus aureus antigens.[3]

References