Differences in autoantibody response to Th/To between systemic sclerosis and other autoimmune diseases

Objective: To examine differences in autoantibody response and immunogenetic background between patients with systemic sclerosis (SSc) and those with other autoimmune diseases who had serum anti-Th/To antibodies. Methods: Serum samples from 1048 Japanese patients with various autoimmune diseases were screened for anti-Th/To antibodies using RNA and protein immunoprecipitation assays. The reactivity to RNase P subunits was examined by immunoprecipitating ³⁵S labelled recombinant Rpp38, Rpp30, and hPop1 produced by in vitro transcription and translation. HLA-DRB1, DQB1, and DPB1 alleles were identified using a polymerase chain reaction followed by a restriction fragment length polymorphism assay. Results: Serum anti-Th/To antibodies were detected in 14 of 303 patients with SSc and seven of 745 patients without SSc (4.6% v 0.9%; p=0.0003). Similar percentages of patients with and without SSc showed immunoreactivity to Rpp38 and Rpp30, but more patients with SSc than patients without SSc showed a reactivity to hPop1 (93% v 14%; p=0.002). In patients with anti-Th/To antibodies DRB1*1502 or *0802 was detected more often, and the DRB1*0405-DQB1*0401 haplotype less often in patients with SSc than in patients without SSc (79% v 14%, p=0.02, and 7% v 71%, p=0.01, respectively). Conclusions: Anti-Th/To antibodies were detected in a small proportion of autoimmune patients lacking clinical features related to SSc. A close relationship between disease expression and anti-hPop1 reactivity as well as HLA class II alleles in anti-Th/To positive patients suggests that the process of anti-Th/To antibody production may be different between patients with and those without SSc.