ANA Patterns

AC-9 - Clumpy nucleolar


Previous Nomenclature	None
Description	Irregular staining of the nucleoli and Cajal bodies with a peri-chromosomal staining at the metaphase plates. e.g. anti-fibrillarin.
Antigen Association	U3-snoRNP/fibrillarin

Clinical Relevance
First level information
About Clinical Relevance & List of Abbreviations

▶

Found in patients with SSc (48)

▶

If SSc is clinically suspected, it is recommended to perform a follow-up test for anti-U3RNP/fibrillarin antibodies; the antigen is included in disease specific immunoassays (i.e., SSc profile*) (48)

▶

If confirmed as anti-U3RNP/fibrillarin reactivity by immunoassay, the clinical association is with diffuse SSc, increased incidence of pulmonary arterial hypertension, skeletal muscle disease, severe cardiac involvement, and gastrointestinal dysmotility (23, 48–50)

▶

Among SSc patients, anti-U3RNP/fibrillarin antibodies are most commonly found in African American and Latin American patients (48, 49, 51)

Notes: Although some anti-U3RNP/fibrillarin immunoassays are commercially available, technical issues relating to the limited sensitivity of these immunoassays should be taken into consideration (24).

*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

23.

Johnson SR, Fransen J, Khanna D, et al. Validation of potential classification criteria for systemic sclerosis. Arthritis Care Res 2012;64:358-67.

24.

Mehra S, Walker J, Patterson K, et al. Autoantibodies in systemic sclerosis. Autoimmun Rev 2013;12:340-54.

48.

Okano Y, Steen VD, Medsger TA. Autoantibody to U3 nucleolar ribonucleoprotein (fibrillarin) in patients with systemic sclerosis. Arthritis Rheum 1992;35:95-100.

49.

Arnett FC, Reveille JD, Goldstein R, et al. Autoantibodies to fibrillarin in systemic sclerosis (scleroderma). An immunogenetic, serologic, and clinical analysis. Arthritis Rheum 1996;39:1151-60.

50.

Tormey VJ, Bunn CC, Denton CP, et al. Anti-fibrillarin antibodies in systemic sclerosis. Rheumatology 2001;40:1157-62.

51.

Nandiwada SL, Peterson LK, Mayes MD, et al. Ethnic differences in autoantibody diversity and hierarchy: More clues from a US cohort of patients with systemic sclerosis. J Rheumatol 2016;43:1816-24.

Second level information

None

Second level information references

None

FAQ

Discrepancy in HEp-2 IFA and western blot data. How do you explain the detection of antibodies by western blot (WB) that are not related to the pattern observed in HEp-2 cells by indirect immunofluorescence (IFA)?

This is not an uncommon phenomenon and there are several possible explanations for this apparent discrepancy.

It is recognized that each immunoassay platform (IFA, WB, ELISA, immunoprecipitation (IP), etc.) is dependent upon a given set of epitopes of relevant autoantigens (1). Broadly, autoantibodies recognize linear and/or discontinuous (native or conformational) epitopes. In the context of discontinuous epitopes, it is important to appreciate that many target autoantigens are part of macromolecular complexes where unique epitopes might be represented as quaternary structures. Immunoassays where the epitope structures are best preserved include IP of cell lysates and HEp-2 IFA. However, there is an important caveat for HEp-2 IFA because the cells have been fixed in methanol and/or acetone (or other undisclosed â€˜trade secretâ€™ fixatives) that likely alter some epitopes as well as well as exposing others. As to the question of native epitope preservation, WB presents the largest challenge because the protocols of boiling proteins under deliberate denaturing conditions most likely alters epitopes significantly. It is true that some may renature/refold after electro-transfer of proteins to nitrocellulose membrane, but many most likely do not. When â€œantibodies by blotâ€ are â€œnot related to the pattern observed in HEp-2 cells by IFA,â€ one explanation is that antibodies to epitopes recognized in IFA are not identical to or represent only a proportion of those (or even different ones) recognized in a WB. One example for this is anti-fibrillarin; IFA typically shows an AC-9 pattern and yet negative in immunoblot because a high percentage of anti-fibrillarin antibodies do not recognize denatured fibrillarin in immunoblot.

It is common that a given serum sample (especially in SLE) has more than one autoantibody specificity. Hence, another explanation is that when two (or more) completely different antibody specificities co-exist in the same sera, confounding results can be observed, especially on the HEp-2 IFA. In that case, the HEp-2 IFA pattern may reflect the combination of IFA reactivity of all present autoantibodies and the resultant pattern may be different from the one expected if there were only one autoantibody specificity in the serum.

1. Mahler M, Bluthner M, Pollard KM. Advances in B-cell epitope analysis of autoantigens in connective tissue diseases. Clin Immunol. 2003 May;107:65-79.

Date: August 14, 2020