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.