Densely distributed but distinct grains seen in the nucleoli of interphase cells. In metaphase cells, up to 5 bright pairs of the nucleolar organizer regions (NOR) can be seen within the chromatin body. The cytoplasm of mitotic cells may be slightly positive. e.g. anti-NOR-90, anti-RNA polymerase I.
RNA polymerase I, hUBF/NOR-90
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The AC-10 pattern can be seen in various conditions, including SSc, Raynaud’s phenomenon, SjS, and cancer.
If the AC-10 pattern is observed in the serum of patients with conditions mentioned above, follow-up testing for anti-NOR90 (hUBF) antibodies is to be considered; the antigen is included in disease specific immunoassays (i.e. SSc profile).
While AC-10 is associated with anti-RNApol I antibodies, these antibodies almost always coexist with anti-RNApol III antibodies which reveal the AC-5 pattern; therefore, if SSc is clinically suspected, it is recommended to perform a follow-up test for anti-RNApol III antibodies (See also AC-5); specific immunoassays for anti-RNA pol I antibodies are currently not commercially available.
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