[A new autoantibody anti-Na which reacts with a cell cycle-dependent nuclear antigen]

By immunofluorescent techniques many autoantibodies have been detected in sera from patients with connective tissue diseases. A distinct antinuclear antibody reacting with a cellular component which showed a characteristic expression pattern is reported. The new antibody, termed anti-Na, stained approximately 20-30% of the HEp-2 cell with a variegated speckled pattern. In synchronized cell analysis, anti-Na showed fine speckles in G2/M phase cells, discrete speckles in dividing chromosomes, and specific cytoplasmic staining in anaphase and telophase cells. Although the preliminary study showed that 3% of SLE patients had anti-Na, the frequency of the anti-Na antibody in rheumatic diseases and their clinical significance remain to be clarified. Screening of a lambda gt11 cDNA expression library with anti-Na antibody yielded only one cDNA encoding a portion of this autoantigen. Deduced amino acid sequences of this cDNA showed a partial homology with myosin heavy chain of C. elegans, suggesting that the Na antigen is involved in contractibility related to myosin.