AC-15 - Cytoplasmic fibrillar linear
Previous Nomenclature actin-like
Description This pattern is characterized by decorated cytoskeletal fibers, sometimes with small, discontinuous granular deposits. Typical staining show striated actin cables spanning the long axis of the cells. e.g. anti-actin, anti-non-muscle myosin.
Antigen Association actin, non-muscle myosin
Clinical Relevance
First level information
About Clinical Relevance & List of Abbreviations

Found in patients with AIH type 1, chronic HCV infection, and celiac disease (IgA isotype); rare in SARD (17)

If AIH type 1 is clinically suspected, it is recommended to confirm reactivity with smooth muscle antibodies (IgG isotype), typically detected by IIFA on rodent tissue (liver, stomach, kidney); anti-smooth muscle antibodies are included in the international criteria for AIH type 1 (17,80)

F-actin is the main target antigen of anti-smooth muscle antibodies in AIH type 1; autoantibodies to F-actin are of more clinical importance than antibodies to G-actin (81–83)

Notes: Although anti-F-actin immunoassays are commercially available, technical issues relating to the sensitivity of these immunoassays should be taken into consideration.
First level information references
Conrad K, Schössler W, Hiepe F. Autoantibodies in organ specific autoimmune diseases. a diagnostic reference. 8. 2th edn. Autoantigens autoantibodies autoimmunity, 2017.
Liberal R, Grant CR, Longhi MS, et al. Diagnostic criteria of autoimmune hepatitis. Autoimmun Rev 2014;13:435-40.
Lidman K, Biberfeld G, Fagraeus A, et al. Anti-actin specificity of human smooth muscle antibodies in chronic active hepatitis. Clin Exp Immunol 1976;24:266-72.
Fusconi M, Cassani F, Zauli D, et al. Anti-actin antibodies: a new test for an old problem. J Immunol Methods 1990;130:1-8.
Chretien-Leprince P, Ballot E, Andre C, et al. Diagnostic value of anti-F-actin antibodies in a French multicenter study. Ann N Y Acad Sci 2005;1050:266-73.
Second level information

High prevalence of IgA and/or IgG type anti-actin antibody has been reported in celiac disease (1, 2)

Autoantibodies to non-muscle myosin have been described in 3 patients with HCV-positive chronic hepatitis/liver cirrhosis (3)

Monoclonal antibodies to non-muscle myosin have been reported in chronic lymphocytic leukemia (4).

Note: Specific immunoassays for non-muscle myosin are currently not commercially available.
Second level information references
Pedreira S, Sugai E, Moreno ML, et al. Significance of smooth muscle/anti-actin autoantibodies in celiac disease. Acta Gastroenterol Latinoam 2005;35:83-93.
Clemente MG, Musu MP, Frau F, et al. Immune reaction against the cytoskeleton in coeliac disease. Gut 2000;47:520-6.
von Muhlen CA, Chan EKL, Peebles CL, et al. Non-muscle myosin as target antigen for human autoantibodies in patients with hepatitis C virus-associated chronic liver diseases. Clin Exp Immunol 1995;100:67-74.
Chu CC, Catera R, Hatzi K, et al. Chronic lymphocytic leukemia antibodies with a common stereotypic rearrangement recognize nonmuscle myosin heavy chain IIA. Blood 2008;112:5122-9.
How to deal with just a “nuclear speckled” IFA report?
In my practice I have followed patients with ANA findings, with a nuclear speckled pattern (without specifying whether fine/dense/coarse), in patients with very heterogeneous phenotypes, some with a clinical picture that suggests further investigation of systemic autoimmune disease (one patient with proximal muscle weakness and skin thickening) and others who represent only non-specific findings. In such situations, as a precaution, I request more specific autoantibodies. However, this pattern (nuclear speckled pattern) is not described by the "ICAP" and I am in doubt about which antigenic association it represents, even to guide which autoantibody may be present and which ones to look after. How to interpret this pattern? Does the lab describe it when it is not possible to "refine" such a conclusion? Could this be associated with deficiency in the methodology, sample, interpretation?
Online since 19 May 2015