Anti-tRNP(ser)sec/SLA/LP autoantibodies. Comparative study using in-house ELISA with a recombinant 48.8 kDa protein, immunoblot, and analysis of immunoprecipitated RNAs.

Background: Antibodies against tRNP((ser)sec) (ribonucleoproteins, RNP) have been described in our laboratory as markers of poor outcome in type 1 autoimmune hepatitis (AIH). The antigenic protein has been sequenced and cloned as a 48.8 kDa protein and identified with soluble liver antigen (SLA) and liver-pancreas (LP) antigen. The aim of this paper was to determine the best assay by which to detect these antibodies in type 1 AIH.
Methods: A simple and reliable enzyme linked immunoassay based on prokaryotically expressed protein was compared with an immunoblot assay using prokaryotically- and eukaryotically-expressed proteins and an assay based on immunoprecipitated RNAs from HeLa cell extracts. Eighty-one sera from 58 patients with type 1 AIH, 168 sera from patients with autoimmune diseases or chronic hepatitis C, and 60 sera from healthy subjects were similarly tested.
Results: The specificity of the assays was 100%, but the frequency of seropositivity was higher in the assay based on immunoprecipitated RNAs (44.4%) than in the enzyme-linked immunosorbent assay (ELISA) (16%) and the immunoblot assay with prokaryotically (12.34%) and eukaryotically (14.8%)-expressed protein. There were no clinical differences between the patients positive by ELISA, immunoblot assay, or immunoprecipitated RNAs.
Conclusions: These results suggest that the analysis of the immunoprecipitated RNAs is the most useful, sensitive and specific method to detect anti-tRNP((ser)sec)/SLA/LP autoantibodies.
(Copyright Blackwell Munksgaard 2005)