This slide is an illustration of a HEp-2 or HEp-2000® cell with several nuclear and cytoplasmic structures indicated. Antibodies to DNA, histones, centromere, nuclear RNP, cytoplasmic RNP, mitochondria, ribosomes, lysosomes, golgi apparatus (as well as a variety of cytoskeletal proteins such as microfilaments, intermediate filaments, and microtubules) can be detected using the HEp-2 or HEp-2000® cell lines. It is important to note that RNA constitutes the bulk of the nucleic acid in the cells, being 5-10 times more abundant than DNA. Generally we consider two compartments in the cell when detecting autoantibodies in systemic rheumatic disease: (1) nucleus, and (2) cytoplasm. Staining of the nucleus includes staining inside the nucleoli.