Cross-reactive epitopes on beta2-glycoprotein-I and Saccharomyces cerevisiae in patients with the antiphospholipid syndrome.

Anti-Saccharomyces cerevisiae antibodies (ASCA), directed against the phosphopeptidomannan (PPM) part of the cell wall of the yeast, have been identified as an important and specific serological marker for Crohn's disease. We evaluated the prevalence and properties of ASCA in APS patients. Thirty-one out of 155 APS patients tested positive for ASCA (20.0%), compared to 5.0% in healthy controls (P < 0.05). The presence of ASCA was not associated with any specific manifestation of APS. The ASCA found to be the population of anti-beta2GPI antibodies (Abs). Affinity purified anti-beta2GPI from ASCA-positive sera on a beta2GPI column, bound specifically the PPM, as shown by direct binding and competition assays (95-98%). The PPM inhibited differentially the anti-beta2GPI binding to beta2GPI. Since the anti-beta2GPI anti-PPM could bind only native form of beta2GPI and not the recombinant form, we assume that these specific anti-beta2GPI subpopulations of Abs are directed to the glycosylated site of the molecule. In conclusion, a subpopulation of anti-beta2GPI is specific to the glycosylated site of the beta2GPI molecule that cross-reacts with PPM.

Identification of target antigen for SLA/LP autoantibodies in autoimmune hepatitis.

BACKGROUND: Autoantibodies are a hallmark of autoimmune hepatitis, but most are not disease specific. Autoantibodies to soluble liver antigen (SLA) and to liver and pancreas antigen (LP) have been described as disease specific, occurring in about 30% of all patients with autoimmune hepatitis, but no standardised assays are available. Methods We tested 2000 serum samples from patients with various liver diseases and controls for SLA autoantibodies by inhibition ELISA. Serum samples positive for SLA antibodies were used for immunoscreening of cDNA expression libraries. Identified clones were tested against a panel of serum samples positive for SLA and LP autoantibodies and control serum samples, and the epitope mapped by deletion mutants and exonuclease digestion. FINDINGS: SLA and LP autoantibodies were identical. Of 2000 serum samples screened, 35 were positive for SLA autoantibodies. These positive samples came from patients with autoimmune hepatitis; three from patients with an overlap syndrome (primary biliary cirrhosis and secondary autoimmune hepatitis). Expression cloning and absorption experiments identified a 422 aminoacid protein present in two splice variants as the sole target antigen. Aminoacids 371-409 were critical for immune recognition. INTERPRETATION: The identified cDNA encodes the primary target antigen of SLA/LP autoantibodies. The SLA/LP antigen has a previously unknown aminoacid sequence, and presumably codes for an unindentified enzyme, suggested to be UGA-suppressor tRNA-associated protein. SLA/LP autoantibodies are disease specific and recognise a dominant epitope, suggesting a specific antigen-driven immune response. Identification of the SLA/LP target antigen will allow establishment of a reliable, widely available diagnostic assay. Furthermore, its role in the pathogenesis of autoimmune hepatitis can now be studied.

Establishment of standardised SLA/LP immunoassays: specificity for autoimmune hepatitis, worldwide occurrence, and clinical characteristics.

BACKGROUND: Antibodies to soluble liver antigen/liver pancreas (SLA/LP) are specific markers of autoimmune hepatitis. Their target antigen has recently been cloned. AIMS: To establish standardised immunoassays using the recombinant antigen, and to assess the frequency and significance of seropositivity in patients from different countries. METHODS: An enzyme linked immunoassay was developed using purified recombinant antigen and validated by testing sera from 200 healthy blood donors and 1026 patients with various liver and non-liver diseases. The assay was then applied to 454 sera from 419 patients with autoimmune hepatitis from different countries. All sera were also tested by inhibition immunoassay and western blot. RESULTS: Antibodies were reliably detected by the recombinant immunoassay and occurred exclusively in patients with autoimmune liver disease. Twenty three of 149 patients from the USA (15%), 23/132 from Brazil (17%), 21/108 from Germany (19%), and 2/30 from Japan (7%) were seropositive. Clinical features at presentation were similar between seropositive and seronegative patients. However, relapse after corticosteroid withdrawal or during maintenance therapy occurred more commonly in seropositive patients. CONCLUSIONS: Antibodies to SLA/LP can be reliably detected by these standardised immunoassays based on recombinant antigen. Antibodies to SLA/LP occur with similar frequencies in different geographical regions, races, and age groups, and are of exquisite diagnostic specificity. Whether SLA/LP positive patients represent a clinically distinct subgroup remains to be determined; relapse during treatment reduction appeared to be more common in the SLA/LP group.