Pleomorphic speckled nucleoplasmic staining, with variability in size and brightness of the speckles. In interphase, some cells are negative (G1 phase), some are intensely stained (S-phase) and some present rare and scattered speckles with occasional nucleolar staining (late S and early G2 phases). Mitotic cells are not stained.
SLE, other conditions.
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The AC-13 pattern has formerly been considered highly specific for SLE, but this specificity is debated.
If SLE is clinically suspected, it is recommended to perform a follow-up test for anti-PCNA antibodies; the antigen is included in several routine ENA profiles.
Recent studies with antigen-specific immunoassays show clinical associations also with SSc, AIM, RA, HCV, and other conditions.
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A major challenge in deriving an association of the AC-13 pattern with antibodies to the classical 35 kDa PCNA (elongation factor of DNA polymerase delta auxiliary protein) is that “PCNA” is known to be a macromolecular complex where targets other than the ‘classical’ 35 kDa PCNA are present. In addition, a number of other apparently unrelated targets can also produce an AC-13-like pattern by HEp-2 IIFA.
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