P-ANCA

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Perinuclear staining typical of p-ANCA

p-ANCA, or MPO-ANCA, or Perinuclear Anti-Neutrophil Cytoplasmic Antibodies, show a perinuclear staining pattern.

This pattern occurs because the vast majority of the antigens targeted by ANCAs are highly cationic (Positively charged) at pH 7.00. During ethanol (pH ~7.0 in water) fixation, antigens which are more cationic migrate and localize around the nucleus, attracted by its negatively charged DNA content. Antibody staining therefore results in fluorescence of the region around the nucleus.

Targets

By far the most common p-ANCA target is myeloperoxidase (MPO), a neutrophil granule protein whose primary role in normal metabolic processes is generation of oxygen radicals.

ANCA will less commonly form against alternative antigens that may also result in a p-ANCA pattern. These include lactoferrin; elastase; and cathepsin G.

When the condition is a vasculitis, the target is usually MPO. However, the proportion of p-ANCA sera with anti-MPO antibodies has been reported to be as low as 12%.

Medical conditions

p-ANCA is associated with several medical conditions:

• It is fairly specific, but not sensitive for ulcerative colitis, so is not useful as a sole diagnostic test. When measured together with Anti-saccharomyces cerevisiae antibodies (ASCA), p-ANCA has been estimated to have a specificity of 97% and a sensitivity of 48% in differentiating patients with ulcerative colitis from normal controls.
• about 50% of cases of Churg-Strauss syndrome
• A majority of primary sclerosing cholangitis
• sometimes polyarteritis nodosa (only in the variant microscopic polyangiitis, usually negative in typical polyarteritis nodosa)
• microscopic polyangiitis
• Focal necrotising and crescentic glomerulonephritis
• Rheumatoid arthritis

See also

• C-ANCA
• Anti-Neutrophil Cytoplasmic Antibody (ANCA)