Human anti-centromere sera recognise a 19.5 kD non-histone chromosomal protein from HeLa cells

Autoimmune sera from 18 scleroderma patients were found to give a centromere positive immunofluorescence response on formaldehyde fixed HeLa cells and on chromosome spreads. Immunoblotting experiments with a protein fraction enriched in HeLa chromosomal proteins revealed that the antigenic target common to all 18 sera is a polypeptide of 19.5 kD. This polypeptide, which is not one of the core histones, is not soluble under conditions which favour the release of nuclear ribonucleoprotein particles. Antigen specific purification of autoantibodies with subsequent immunofluorescence studies confirmed that the 19.5 kD antigen is restricted to cell cycle-dependent single or double spheres at the centromere of HeLa chromosomes. Two additional polypeptides of 23 kD and 25.5 kD immunoreactive with five of the 18 centromere positive sera are not located at the centromere region, suggesting that other autoantibody systems are present in these sera.