Objective: NOR-90 autoantibodies directed against the nucleolus organizer region (NOR) have been described as rare scleroderma associated antibodies. We studied the clinical features of patients with NOR-90 antibodies as well as their HLA phenotype.
Methods: NOR-90 antibodies were detected by indirect immunofluorescence assay using HEp-2 cells, by chromosome spreads as a substrate and in addition by Western blot analysis with HeLa-S3 nucleolar extract. HLA antigens of the NOR-90 antibody positive patients were typed with the standard NIH complement dependent microcytotoxicity test.
Results: Nine sera selected by means of the indirect immunofluorescence revealed a typical double band pattern of about 90 kDa identical with the pattern of 2 NOR-90 reference sera by Western blot analysis. Only one patient positive for NOR-90 antibodies suffered from systemic sclerosis (limited cutaneous scleroderma). The other patients with NOR-90 antibodies showed no signs of systemic sclerosis. All patients with NOR-90 antibodies were women and 8 of 9 patients (89 versus 13% of healthy controls, Pcorr < 0.001) were positive for the HLA-DR1 allele.
Conclusion: In contrast to the first report on NOR-90 antibodies we demonstrated no association of these antibodies with systemic sclerosis; however, we found strong evidence for an immunogenetic background of NOR-90 antibody formation.