What are ANCAs?
ANCAs are antibodies directed against specific antigens present in the cytoplasm of neutrophils. There are three different types of IIF staining patterns for ANCAs using ethanol-fixed neutrophils as substrate:
• C-ANCA pattern: diffuse cytoplasmic staining on immunofluorescence. The most common antibodies causing this pattern are directed against serine PR3. Less commonly, the target antigen is bactericidal/permeability-increasing protein or others.
• P-ANCA pattern: perinuclear staining pattern around the nucleus. The most important antibody causing this pattern is directed against MPO. Other antigen targets include elastase, cathepsin G, lactoferrin, lysozyme, and azurocidin.
• Atypical ANCA pattern: snow-drift staining pattern around nucleus often confused with the P-ANCA pattern. Usually seen in patients with inflammatory bowel disease, connective tissue diseases, or autoimmune hepatitis.