CHARACTERIZATION OF A CELL CYCLE-DEPENDENT NUCLEAR AUTOANTIGEN

Analysis of reactivity to nuclear antigens in autoimmune sera revealed a serum that produced a previously undescribed cell cycle-dependent i mmunofluorescence staining pattern. By indirect immunofluorescence usi ng HEp-2 cells as substrate, the serum generated a speckled and nucleo lar pleomorphic staining pattern. This characteristic immunofluorescen ce pattern was detected in different cell lines from various species i ndicating that the antigen was highly conserved. This serum immunoprec ipitated a 85 kDa protein using an extract from [S-35]-labeled HeLa ce lls. Indirect immunofluorescence of proliferating mouse 3T3 cells disp layed the characteristic pleomorphic staining which was not observed i n serum-starved cells. Resting human and mouse peripheral blood lympho cytes were negative in immunofluorescence while mitogen-stimulated lym phocytes were positive. Germinal centers of mice two weeks after immun ization with 2-phenyl-oxazolone showed speckled immunofluorescence sta ining in the dark zones whereas unimmunized mice were completely negat ive. Cell synchronization experiments showed a characteristic sequence of locations of the antigen during the cell cycle. In G(1), cells wer e completely negative. In late G(1), G(1)/S and S phase, speckles were visible. In early G(2), speckles were visible, and later in G(2), the nucleoli were positive. During mitosis chromosomes were stained. Furt her characterization of this antibody specificity and cloning of cDNA are in progress.