Soluble liver antigen (SLA) antibody detection by ELISA and multiplexing technologies

Abstract

Objective: Develop and evaluate assays for the detection of antibodies to soluble liver antigen (SLA). SLA, also known as liver/pancreas antibody, was found to be 100% specific for autoimmune hepatitis (AIH) in a recent study of 2000 sera collected from individuals with various disease conditions and healthy individuals (Wies et al., Lancet 2000; 355:1510). Although SLA antibodies occur in only about 30% of patients with autoimmune hepatitis, they are found in some individuals with AIH who are negative for other autoantibodies.

Methods: Specimens from patients with autoimmune hepatitis, non-autoimmune liver disease, various autoimmune conditions, as well as specimens from healthy individuals were tested by the INOVA QUANTA Lite™ SLA (Soluble Liver Antigen) ELISA. The ELISA test uses a recombinant SLA antigen. The feasibility of simultaneous detection of antibodies to SLA, LKM-1, and M-2 antibodies was also determined using the QuantaPlex™ test system (Luminex).

Results: Site 1 (San Diego): Testing of 132 specimens from normal, healthy individuals with ages ranging from 5 to 69 years old, resulted in a specificity of 100% (132/132). A second panel, consisting of 10 clinically-defined samples obtained from Dr. Lohse (5 positive and 5 negative), was tested and in complete agreement with the results obtained in the Mainz laboratory by an inhibition ELISA assay and western blot analysis. A panel of 18 specimens positive for various autoimmune or disease antibodies, including GBM, LKM-1, ANA, SLE, M-2 and GPA, were all found to be negative on the SLA ELISA. The multiplex assay was able to clearly discriminate and identify SLA, LKM-1, and M-2 positive samples and offers a promising new methodology for evaluation of patients with suspected liver disease.

Site 2 (Mainz): A panel of 200 sera were tested. These included 32 SLA/LP positive AIH sera, 18 SLA/LP negative AIH sera, 100 sera from viral hepatitis patients, 15 sera from patients with non-AIH liver diseases and sera from 35 patients with various disease conditions. 31 of the 32 SLA positive sera were clearly positive and one was equivocal. Excluding the equivocal result, the sensitivity was 100%.

Conclusions: Our data show that with the exclusion of the 1 equivocal result, the SLA ELISA test had 100% specificity and 100% sensitivity. No cross-reactivity was seen with sera positive for other autoimmune makers. Availability of assays for detection of SLA antibodies will provide a new marker to assist in the diagnosis of patients with autoimmune hepatitis. Detection of SLA antibodies is especially valuable for testing the 10–15% of AIH patients who are negative for conventional autoantibodies.