ICAP
AC-8 - Homogeneous nucleolar
Previous Nomenclature None
Description Diffuse fluorescence of the entire nucleolus, while the metaphase plate shows no staining. e.g. anti-PM-Scl, anti-Th/To.
Antigen Association PM/Scl-75, PM/Scl-100, Th/To, B23/nucleophosmin, nucleolin, No55/SC65
Clinical Relevance
First level information
About Clinical Relevance

Found in patients with SSc, SSc-AIM overlap syndrome, and patients with clinical manifestations of other SARD (44–46)

If limited cutaneous SSc is clinically suspected, it is recommended to perform a follow-up test for anti-Th/To antibodies; the antigen is included in disease specific immunoassays (i.e., SSc profile*) (44, 45)

If SSc-AIM overlap syndrome is clinically suspected, it is recommended to perform a follow-up test for anti-PM/Scl antibody reactivity; the antigen may be included in the routine ENA profile and is included in disease specific immunoassays (i.e., inflammatory myopathy profile* and the SSc profile*); in general, anti-PM/Scl antibodies yield a diffuse nuclear fine speckled staining in addition to the AC-8 pattern (46)

Other antigens recognized include B23/nucleophosmin, No55/SC65, and C23/nucleolin, but the clinical significance of these autoantibodies is not well established; specific immunoassays for these autoantibodies are currently not commercially available

 

Notes: Although some anti-Th/To antibody immunoassays are commercially available, technical issues relating to the limited sensitivity of these immunoassays should be taken in to consideration (44, 47).

*Availability of the inflammatory myopathy profile, the SSc profile and the (extended) liver profile may be limited to specialty clinical laboratories.

First level information references
44.
Mahler M, Fritzler MJ, Satoh M. Autoantibodies to the mitochondrial RNA processing (MRP) complex also known as Th/To autoantigen. Autoimmun Rev 2015;14:254–7.
45.
Ceribelli A, Cavazzana I, Franceschini F, et al. Anti-Th/To are common antinucleolar autoantibodies in Italian patients with scleroderma. J Rheumatol 2010;37:2071–5.
46.
Mahler M, Raijmakers R. Novel aspects of autoantibodies to the PM/Scl complex: clinical, genetic and diagnostic insights. Autoimmun Rev 2007;6:432–7.
47.
Mahler M, Gascon C, Patel S, et al. Rpp25 is a major target of autoantibodies to the Th/To complex as measured by a novel chemiluminescent assay. Arthritis Res Ther 2013;15.
Second level information

The AC‐8 pattern that is the result of the anti‐Th/To reactivity is also seen in patients with SLE, UCTD (i.e., patients with rheumatic symptoms without a SARD diagnosis), SSc sine scleroderma, idiopathic interstitial lung disease or pulmonary hypertension (20, 21)

Patients with autoantibodies revealing the AC‐8 pattern due to anti‐PM/Scl reactivity may have, in addition to the clinical features of AIM and SSc, various clinical manifestations of SLE and SjS (22)

Second level information references
20.
Fischer A, Pfalzgraf FJ, Feghali‐Bostwick CA, et al. Anti‐Th/To‐Positivity in a Cohort of Patients with Idiopathic Pulmonary Fibrosis. J Rheumatol 2006;33:1600‐1605.
21.
Fischer A, Meehan RT, Feghali‐Bostwick CA, et al. Unique characteristics of systemic sclerosis sine scleroderma‐associated interstitial lung disease. Chest 2006;130:976‐981.
22.
Mahler M, Raijmakers R. Novel aspects of autoantibodies to the PM/Scl complex: clinical, genetic and diagnostic insights. Autoimmun Rev 2007;6:432‐437.
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Online since 19 May 2015