Clinical Information

Autoantibodies targeting antigens in the nuclear region in the human epithelial type 2 (HEp-2) cell line substrate using the indirect immunofluorescence assay (IFA) have traditionally been called antinuclear antibodies (ANA). ANA is a commonly performed antibody test in the initial evaluation of patients with systemic autoimmune rheumatic diseases (also referred to as connective tissue disease). Classic ANA-associated rheumatic diseases include systemic lupus erythematosus (SLE), mixed connective tissue disease, Sjogren syndrome (Sjs), and systemic sclerosis (SSc) including CREST (calcinosis, Raynaud phenomenon, esophageal dysmotility, sclerodactyly, telangiectasia), and inflammatory myopathies (IM) such as dermatomyositis.(1-4) Testing for ANA may also be of diagnostic relevance in the differential evaluation of autoimmune liver diseases (ALD).(5-6)

Classical ANA patterns (antibodies targeting the nuclear region) include homogeneous, speckled, centromere, nuclear dots, and nucleolar. These patterns are routinely reported by most clinical laboratories. Patients with SLE, SSc, Sjs, IM (such as anti-synthetase syndrome and necrotizing autoimmune myopathy), or ALD have also been shown to have clinically significant antibodies that react with antigens in other cellular compartments such as the cytoplasm and structures associated mitosis or mitotic patterns with HEp-2 substrate.(1-3) Based on the increasing recognition of these non-nuclear antigenic targets and their documented clinical relevance, the First International Consensus on ANA Patterns established a classification tree for ANA with alpha-numeric anti-cell (AC) code for each pattern with a recommendation for a change in terminology from antinuclear antibody to anti-cellular antibody.(2) These changes are relevant as, in addition to the nuclear patterns, the classification includes cytoplasmic and mitotic patterns with descriptions for their interpretation, associated antibody targets, and clinical associations when available.(4)

The diagnosis of ANA-associated rheumatic diseases is usually based on a set of criteria of which the presence of anti-cellular antibody or specific associated antibodies may be components. Of all ANA-associated rheumatic diseases, the presence of anti-cellular antibodies is considered a mandatory entry criterion by the 2019 European League Against Rheumatism and the American College of Rheumatology classification criteria for SLE.(7) Since cytoplasmic staining patterns may be reported as "ANA negative" or as a comment with no quantitative or titer result, some patients with clinicopathological symptoms consistent with neuropsychiatric SLE would not qualify for entry based on where testing is performed.(8-10) This limitation may therefore exclude patients who may meet the clinical and other laboratory criteria for disease but are not reported as "ANA positive" due to the use of the current terminology. In an international inception cohort of newly diagnosed SLE patients, 6.2% were anti-cellular antibody-negative with 1.5% testing positive for isolated cytoplasmic or mitotic pattern.(11) In addition, a recent investigation of various HEp-2 IFA kits showed variabilities in the expression of specific patterns with high reproducibility between tests for centromere, multiple nuclear dots, nuclear coarse speckled, nuclear homogeneous and cytoplasmic reticular AMA (antimitochondrial antibody) patterns.(12)

Overall, the anti-cellular antibody is a good screening test for ANA-associated rheumatic diseases with variable sensitivities in the different clinical subsets but lacks diagnostic specificity.(1-4) Therefore, positive results require confirmation with the use of specific ANA-associated antibody tests except for the centromere pattern, which is very characteristic for patients with limited diffuse SSc. Confirmation of a positive anti-cellular antibody test result may be guided by HEp-2 IFA patterns or titer, patient's clinical presentation, or, in some cases, the patient's demographic.(13)