What is "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.