ICAP
AC-29 - DNA topoisomerase I (topo I)-like
Synonym Scl-70-like, Scl-86, DNA Topo I
Antigen Association DNA topoisomerase I
Disease Association systemic sclerosis
Description

The Topo I-like pattern can comprise staining of five subcellular regions:

1) Prominent fine speckled AC-4 type nuclear staining in interphase cells.
2) Consistent strong fine speckled staining of condensed chromatin in mitotic cells. Depending on the serum dilution used, the mitotic chromatin staining may appear homogeneous.
3) Strong staining of nucleolar organizing region (NOR) associated on condensed chromosomes in mitotic cells. This NOR staining may be obscured by the bright chromosomal staining as NORs are not always on the same focal plane (see figure below).
4) Weak cytoplasmic staining in interphase (and mitotic) cells depicts a delicate network radiating from the perinuclear area towards the plasma membrane; in general, during titering sera to higher dilutions relatively more prominent cytoplasmic staining can be observed.
5) Variable nucleolar staining that can appear as a punctate nucleolar or perinucleolar staining in interphase cells. Nucleolar staining is not a universal feature of this pattern.

This 5-element compound staining pattern has been observed in most commercial HEp-2 cell slides1, but there may be some variations in the expression of each element according to the slide brand. The detection of all 5 elements may be a challenge especially when only using a single serum dilution (e.g. strong mitotic chromatin staining obscures NOR) or in many semi-automated systems when images are often selected on a single focal plane (e.g. NOR or cytoplasmic staining not in same focal plane as interphase nuclei).

Practical recommendation how to routinely screen for AC-29 with a HEp-2 slide that show this pattern using a traditional microscope setting: if the above 1) and 2) features are observed on routine samples suggestive of the AC-29, the next step should be to look for 3) positive NOR staining by searching different focal planes for NORs on mitotic chromatins. Next, the presence of the 4) cytoplasmic staining and lastly 5) the nucleolar staining should be evaluated. In some HEp-2 slides, the nucleolar staining is only visible near the edge of the well.

References

Dellavance A, Gallindo C, Soares MG, da Silva NP, Mortara RA, Andrade LE. Redefining the Scl-70 indirect immunofluorescence pattern: autoantibodies to DNA topoisomerase I yield a specific compound immunofluorescence pattern. Rheumatology (Oxford). 2009;48:632-7.

Andrade LEC, Klotz W, Herold M, Conrad K, Ronnelid J, Fritzler MJ, von Muhlen CA, Satoh M, Damoiseaux J, de Melo Cruvinel W, Chan EKL. International consensus on antinuclear antibody patterns: definition of the AC-29 pattern associated with antibodies to DNA topoisomerase I. Clin Chem Lab Med. 2018;56:1783-8.

INOVA HEp-2 images illustrating the AC-29 pattern with staining in all 5 compartments. Panel A is a merged image from the other 3 panels (A', A'', A''') representing different optical sections/focal planes, each illustrating the unique stained structures not obvious in the other focal planes. In addition to the obvious nucleoplasmic and mitotic condensed chromatin staining, panel A' illustrates two bright NORs in focus (arrow) on condensed chromatin in the mitotic cell; panel A'' shows another NOR in focus (arrow) in the same cell; A''' shows characteristic cytoplasmic (arrowhead) and weak perinucleolar staining (short arrow).

Online since 19 May 2015