ICAP
AC-19 - Cytoplasmic dense fine speckled
Previous Nomenclature cytoplasmic homogeneous
Description The pattern appears cloudy, almost homogeneous throughout the cytoplasm. e.g. anti-PL-7.
Antigen Association PL-7, PL-12, ribosomal P proteins
Clinical Relevance
First level information
About Clinical Relevance

Found in patients with SLE and the anti-synthetase syndrome (a subset of AIM), interstitial lung disease, polyarthritis, Raynaud’s phenomenon, and mechanic’s hands; these features may occur in various combinations or as an isolated manifestation, especially interstitial lung disease (33, 86, 87)

If SLE is clinically suspected, follow-up tests for antibodies to ribosomal P phosphoproteins (P0, P1, P2, C22 RibP peptide) are recommended; these antigens may be included in the routine ENA profile

Anti-RibP antibodies have been associated in some studies with neuropsychiatric lupus, and in childhood-onset SLE with autoimmune hemolytic anemia (86, 88, 89)

If AIM, in particular the anti-synthetase syndrome, is suspected, it is recommended to perform follow-up tests for antibodies to tRNA synthetases; antigens are included in disease specific immunoassays (i.e., inflammatory myopathy profile*) (26, 33)

If AIM, in particular necrotizing myopathy, is suspected, it is recommended to perform follow-up tests for anti-SRP antibodies; the antigen is included in disease specific immunoassays (i.e., inflammatory myopathy profile*) (26)

 

Notes: The fine distinction between AC-19 and -20 may depend on HEp-2 substrates and/or antibody concentration; antibodies to both RibP as well as tRNA synthetases may be undetected in HEp-2 IIFA-screening.

*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
26.
Betteridge Z, McHugh N. Myositis-specific autoantibodies: an important tool to support diagnosis of myositis. J Intern Med 2016;280:8–23.
33.
Satoh M, Tanaka S, Ceribelli A, et al. A comprehensive overview on myositis-specific antibodies: new and old biomarkers in idiopathic inflammatory myopathy. Clin Rev Allergy Immunol 2017;52:1–19.
86.
Sciascia S, Bertolaccini ML, Roccatello D, et al. Autoantibodies involved in neuropsychiatric manifestations associated with systemic lupus erythematosus: a systematic review. J Neurol 2014;261:1706–14.
87.
Yura H, Sakamoto N, Satoh M, et al. Clinical characteristics of patients with antiaminoacyl-tRNA synthetase antibody positive idiopathic interstitial pneumonia. Respir Med 2017;132:189–94.
88.
Valões CC, Molinari BC, Pitta AC, et al. Anti-ribosomal P antibody: a multicenter study in childhood-onset systemic lupus erythematosus patients. Lupus 2017;26:484–9.
89.
Mahler M, Kessenbrock K, Szmyrka M, et al. International multicenter evaluation of autoantibodies to ribosomal P proteins. Clin Vaccine Immunol 2006;13:77–83.
Second level information

Autoantibodies to RibP:

Anti-RibP antibodies have been reported in 10% of AIH patients without clinical or laboratory evidence of SLE (33)

The prevalence of anti-RibP antibodies in SLE has been reported to range between 8 – 35% in a multicenter study (34)

Less than 60% of the sera positive for anti-RibP antibodies have the AC-19 pattern at serum screening dilutions of 1/80 or higher; the coexistence of a weak nucleolar staining is relatively common

Autoantibodies to tRNA-synthetases:

Less than 50% of sera having anti-tRNA synthetase antibodies have an AC-19 pattern at serum screening dilutions of 1/80 or higher (35)

 

Note: Most reports describing clinical association of anti-RibP antibodies do not actually show correlations with the AC-19 pattern as such.

Second level information references
33.
Calich AL, Viana VS, Cancado E, et al. Anti-ribosomal P protein: a novel antibody in autoimmune hepatitis. Liver Int 2013;33:909-13.
34.
Mahler M, Kessenbrock K, Szmyrka M, et al. International multicenter evaluation of autoantibodies to ribosomal P proteins. Clin Vaccine Immunol 2006;13:77-83.
35.
Fritzler MJ, Choi MY, Mahler M. The anti-nuclear antibody (ANA) test in the diagnosis of anti-synthetase syndrome and other autoimmune myopathies (AIM). J Rheumatol 2018;45:444-5.
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Online since 19 May 2015