International consensus on antinuclear antibody patterns: definition of the AC-29 pattern associated with antibodies to DNA topoisomerase I

Luis E. C. Andrade*, Werner Klotz, Manfred Herold, Karsten Conrad, Johan Ronnelid, Marvin J. Fritzler, Carlos A. von Muhlen, Minoru Satoh, Jan Damoiseaux, Wilson de Melo Cruvinel, Edward K. L. Chan, Executive Comm ICAP

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review


The indirect immunofluorescence assay (IFA) on HEp-2 cells is the reference method for autoantibody screening. The HEp-2 IFA pattern provides useful information on the possible autoantibodies in the sample. The International Consensus on Antinuclear Antibody Patterns (ICAP) initiative seeks to define and harmonize the nomenclature of HEp-2 IFA patterns. The most relevant and usual patterns have been assigned an alphanumeric code from anti-cell (AC)-1 to AC-28 and were organized into a classification algorithm ( The systemic sclerosis-associated autoantibodies to DNA topoisomerase I (Topo I) produce a peculiar composite 5-element HEp-2 IFA pattern (Topo I-like pattern) comprising the staining of the nucleus, metaphase chromatin plate, nucleolar organizing region, cytoplasm and nucleolus. In a recent assessment of the European Consensus Finding Study Group on autoantibodies, a well-defined anti-Topo I sample was blindly analyzed and classified according to ICAP AC patterns by 43 participant laboratories across Europe. There were wide variations among these laboratories in reporting nuclear, nucleolar and cytoplasmic patterns, indicating the inadequacy of the existing AC patterns to report the Topo I-like pattern. Several ICAP member laboratories independently demonstrated the overall consistency of the HEp-2 IFA Topo I-like pattern using HEp-2 slides from different manufacturers. The ICAP committee reviewed 24 candidate images and selected the four most representative images to be available on the ICAP website. The proper recognition of the AC-29 pattern should trigger suspicion of the presence of anti-Topo I antibodies, which may engender appropriate analyte-specific reflex tests to confirm the autoantibody specificity.
Original languageEnglish
Pages (from-to)1783-1788
Number of pages6
JournalClinical Chemistry and Laboratory Medicine
Issue number10
Publication statusPublished - 1 Oct 2018


  • antinuclear antibodies
  • autoantibodies
  • HEp-2 cell
  • indirect immunofluorescence
  • SCL-70
  • SERA


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