Clinical, laboratory and genetic markers associated with erosions and remission in patients with early inflammatory arthritis: a prospective cohort study.

We investigated the relationship between clinical, laboratory and genetic markers and outcome measures in 159 patients with recent onset of inflammatory arthritis (IA). The majority of patients were managed in community-based rheumatology practice. Median duration of arthritis at baseline was 3 months with median follow-up of 4.0 years (range 0-10). Markers of disease activity and 1987 ACR criteria for rheumatoid arthritis (RA) were estimated every 6 months for the first 2 years and annually thereafter. Presence of shared epitopes (SE) was established by PCR-based method. Main outcome variables were attainment of remission and presence of erosions on X-rays of hands and feet at 3 years. Remission was seen in 34.3% of patients and was independently related to age 60 and older (odds ratio (OR) 3.2; 95% confidence interval (CI), 1.2-8.7) and inversely to the presence of rheumatoid factor (RF) (OR 8.3; 95% CI, 3.2-21.3 for persistent arthritis). Patients with two SE were likely to have persistent arthritis (P=0.006), but this was not significant when corrected for RF. Independent predictors for erosions at 3 years were RF (OR 7.5; 95% CI, 1.9-29.5) and area under the curve for number of swollen joints (OR 1.08; 95% CI, 1.02-1.16). SE status was not predictive of erosions at 3 years (OR 1.6; 95% CI, 0.7-3.7). In univariate analysis, patients possessing DERAA motif on DRB1 were less likely to have erosive disease than without this motif at 4 years (OR 0.21; 95% CI, 0.0-0.9, P=0.037) but this finding was partly explained by adjusting for RF (adjusted OR 0.24; 95% CI 0.04-1.37). In this study of recent onset IA, active disease and RF were associated with poor outcome. Whilst SE did not predict erosive disease, patients with DERAA motif may be protected against erosions whilst the presence of two SE alleles suggests persistence of arthritis.

Autoantibodies to the islet cell antigen SOX-13 are associated with duration but not type of diabetes.

AIMS: The autoantigen SOX-13 of the SRY-related high mobility group box is a low-frequency reactant in sera from patients with Type 1 diabetes. We further investigated the potential diagnostic role of anti-SOX-13, and in particular its ability to distinguish Type 1 from Type 2 diabetes, in two large, well-characterized cohorts. METHODS: SOX-13 autoantibody status was ascertained using a radioimmunoprecipitation assay in (i) a random sample of 546 participants in an Australian community-based study (the Fremantle Diabetes Study; FDS) of whom 119 had Type 1 and 427 Type 2 diabetes, and (ii) a sample of 333 subjects with Type 2 diabetes from the United Kingdom Prospective Diabetes Study (UKPDS) stratified by age, anti-glutamic acid decarboxylase (GAD) and islet cell antibody (ICA) status, and requirement for insulin therapy within 6 years of diagnosis. RESULTS: The frequencies of anti-SOX-13 in the FDS subjects were 16.0% and 14.8% for Type 1 and Type 2 patients, respectively, and levels were similar. In the UKPDS subjects, the frequency was 4.5%. In a logistic regression model involving demographic, anthropometric and metabolic variables, only diabetes duration was significantly associated with anti-SOX-13 positivity, especially for duration > 5 years (P < 0.002). When the coexistence of autoantibodies was assessed in the two study samples, there were no significant associations between anti-SOX-13 and ICA, anti-GAD or ICA512/IA-2. CONCLUSIONS: Whilst the frequency of anti-SOX-13 may be increased in some populations of diabetic patients, this reactivity does not usefully distinguish Type 1 from Type 2 diabetes. However, the association with diabetes duration suggests that anti-SOX-13 may be a non-specific marker of tissue damage associated with chronic hyperglycaemia.

A comparative study of antibody expressions in primary biliary cirrhosis and autoimmune cholangitis using phage display.

Primary biliary cirrhosis (PBC) and autoimmune cholangitis (AIC) are serologic expressions of an autoimmune liver disease affecting biliary ductular cells. Previously we screened a phage-displayed random peptide library with polyclonal IgG from 2 Australian patients with PBC and derived peptides that identified a single conformational (discontinuous) epitope in the inner lipoyl domain of the E2 subunit of the pyruvate dehydrogenase complex (PDC-E2), the characteristic autoantigen in PBC. Here we have used phage display to investigate the reactivity of PBC sera from 2 ethnically and geographically distinct populations, Japanese and Australian, and the 2 serologic expressions, PBC and AIC. Random 7-mer and 12-mer peptide libraries were biopanned with IgG from 3 Japanese patients with PBC and 3 with AIC who did not have anti-PDC-E2. The phage clones (phagotopes) obtained were tested by capture enzyme-linked immunosorbent assay (ELISA) for reactivity with affinity-purified anti-PDC-E2, and compared with those obtained from Australian patients with PBC. Peptide sequences of the derived phagotopes and sequences derived by biopanning with irrelevant antisera were aligned to develop a guide tree based on physicochemical similarity. Both Australian and Japanese PBC-derived phagotopes were distributed in branches of the guide tree that contained the peptide sequences MH and FV previously identified as part of an immunodominant conformational epitope of PDC-E2, indicating that epitope selection was not influenced by the racial origin of the PBC sera. Biopanning with either PBC or AIC-derived IgG yielded phagotopes that reacted with anti-PDC-E2 by capture ELISA, further establishing that there is a similar autoimmune targeting in PBC and AIC.

Expression of protein tyrosine phosphatase-like molecule ICA512/IA-2 induces growth arrest in yeast cells and transfected mammalian cell lines.

The ICA512/IA-2 molecule, a protein with similarity to receptor-type protein tyrosine phosphatases, was discovered during studies to identify autoantigens in Type 1 diabetes. The biological function of ICA512/IA-2 is unknown. We describe striking effects of ICA512/IA-2 on viability and growth of both yeast cells and cultured mammalian cells. In transformed yeast Saccharomyces cerevisiae cells, expression of ICA512/IA-2 induced growth retardation as judged by measurements of optical density and counts of colony-forming units. In contrast, expression of the intracellular domain (amino acids 600-979) of ICA512/IA-2 in yeast or mammalian cells had no such effects. In investigations on apoptosis, expression of ICA512/IA-2 in yeast cells caused loss of plasma membrane asymmetry, but not release of cytochrome c from mitochondria which did occur in a control system after expression of the pro-apoptotic molecule Bax. Possible interactions between ICA512/IA-2 and components of the cytoskeleton were not supported by studies on staining of fixed yeast cells with phalloidin-Texas Red. With transfected mammalian cell lines COS-7 and NIH3T3, expression of ICA512/IA-2 likewise induced growth arrest, with some of the morphological features of apoptosis. Thus obligatory expression of ICA512/IA-2 in eukaryotic cells causes disruption of cellular activities, with growth arrest in yeast and nuclear pycnosis/fragmentation in mammalian cells. A possible explanation is that growth inhibition reflects a part of the presently unknown function of ICA512/IA-2.

Post-panning computer-aided analysis of phagotope collections selected with neurocysticercosis patient polyclonal antibodies: separation of disease-relevant and irrelevant peptide sequences.

The homology of peptide sequences selected from a 7mer phage display library with antibodies elicited by the multicelled parasite Taenia solium in cerebrospinal fluid and serum of neurocysticercosis (NCC) patients and by antibodies of uninfected control patients with similar neurological complications of other ethiology (non-NCC) were analyzed using a PILEUP-Tudos sequence alignments program. The analysis generated dendrograms bearing two types of sequence clusters, those containing (1) only NCC patients-derived peptides and (2) both NCC- and control non-CC -- patient derivatives. By using ELISA, peptides that were selected by the antibodies were identified predominantly in the NCC-derived clusters. In repeated analysis in which sequences were added or removed, the first type of clusters maintained their structure, while the second type of clusters were split into many separate homology units dispersed throughout the guide tree. These results are interpreted as the ability of the analysis to segregate NCC-specific peptide sequences from other sequences. Altogether, this study demonstrates the high potential of the PILEUP-Tudos computer program to analyze phagotope collections recovered through biopanning with polyclonal antibodies elicited in patients by complex and as yet unknown multiple pathogenic antigens and to separate all phagotopes that are disease-relevant on the basis of the sequence homology.

Antibodies to diabetes-associated autoantigens in Indian patients with Type 1 diabetes: prevalence of anti-ICA512/IA2 and anti-SOX13.

We ascertained frequencies of autoantibodies to a suite of islet cell antigens including ICA512/IA2 and SOX13 in Asian Indians with Type 1 diabetes and in other forms of diabetes. Autoantibodies to ICA512/IA2 and SOX13 were tested by radioimmunoprecipitation assay, and results were amalgamated with previous data on antibodies to glutamic acid decarboxylase (GAD) and to islet cell cytoplasmic antigens (ICA). The frequency of anti-SOX13 was higher in Asian Indians than in Europids. Overall, the combined frequency for all autoantibodies to diabetes-associated antigens in Type 1 diabetes in Indians approached the frequency reported for Europids. There was an unexpectedly high frequency of autoantibody reactions to any one of the autoantigens tested (24%) in fibrocalculous pancreatic diabetes, however, individual autoantibody frequencies were relatively low. Our data indicate that, whatever the population studied, testing for multiple autoantigenic reactivities is more informative than more limited testing, and that there may be regional (presumably ethnically based) differences in levels of particular autoantibodies in cases of Type 1 diabetes.

Antibodies to SOX13 (ICA12) are associated with type 1 diabetes.

SOX13 is an islet cell autoantigen (ICA12), identified by antibody screening of an islet cDNA library, using sera from patients with Type 1 diabetes. We ascertained the frequency of antibody reactivity to SOX13 and compared it with other Type 1 diabetes autoantibody reactivities. Antibodies were measured by radioimmunoprecipitation (RIP) using (35) S labelled SOX13 expressed in rabbit reticulocyte lysate. Sera from 109 subjects with Type 1 diabetes, 29 with Type 2 diabetes, 144 with other autoimmune diseases and from 201 controls were tested for anti-SOX13, and results were compared with the frequency of antibodies to glutamic acid decarboxylase (anti-GAD), islet cell antigen 512 (anti-ICA512) and islet cell cytoplasm (ICA). Anti-SOX13 were detected in 20 (18.3%) of 109 subjects with Type 1 diabetes, and more frequently in adults than in children (29% vs 10%). Anti-SOX13 usually occurred with anti-GAD but rarely with anti-ICA512. Seven sera positive for anti-SOX13 did not react with either GAD, ICA512 or islet cell cytoplasm indicating that anti-SOX13 represented a distinct population of antibodies. Reactivity to SOX13 represents a further autoantibody response in adults with Type 1 diabetes and may provide a useful disease marker in subjects in whom other autoantibody tests are negative.

Antimitochondrial autoantibodies in saliva and sera from patients with primary biliary cirrhosis.

BACKGROUND AND AIMS: Primary biliary cirrhosis (PBC) is a cholestatic autoimmune liver disease characterized by antimitochondrial autoantibodies (AMA) in serum, for which the reactants are E2 subunits of the three 2-oxoacid dehydrogenase (2-OAD) enzymes, particularly pyruvate dehydrogenase complex (PDC-E2). Some 70% of patients with PBC have a coexisting autoimmune disease including Sjögren's syndrome. We aimed to ascertain the frequency and isotype of AMA in saliva in PBC. METHODS: Serum and saliva from 12 patients with PBC were tested for AMA by immunoblotting on bovine heart mitochondria, and by an automated microassay based on inhibition of the enzymatic activity of PDC. RESULTS: Autoantibodies of the immunoglobulin (Ig)G, IgM, and IgA immunoglobulin isotypes against the E2 subunits of 2-OAD enzymes were demonstrable in PBC in serum (12 of 12 cases) and saliva (nine of 12 cases). Salivary autoantibodies, like serum autoantibodies, were predominantly reactive with PDC and of the IgG isotype. Results for serum and saliva corresponded closely with regard to reactivity with individual enzymes of the 2-OAD enzyme family, and to the autoantibody isotype that was predominantly expressed, and also in the capacity to inhibit the enzymatic activity of PDC. CONCLUSIONS: The presence of AMA in saliva to 2-OAD enzymes indicates that salivary glands could participate in the pathogenetic process of PBC. The detection of salivary AMA by a semi-automated enzyme inhibition assay offers possibilities for rapid population screening for detection of preclinical PBC among at-risk individuals, middle-aged to older women.

Automated enzymatic mitochondrial antibody assay for the diagnosis of primary biliary cirrhosis.

Primary biliary cirrhosis is a progressive autoimmune disease that affects middle aged women, resulting in liver cirrhosis. We describe here an automated enzymatic mitochondrial antibody assay adapted for performance on laboratory analysers for the serological diagnosis of primary biliary cirrhosis. This assay detects the characteristic autoantibody directed against the 74kDa E2 subunit of the pyruvate dehydrogenase complex. Analysis of receiver operator characteristic curve data indicated that the automated enzymatic mitochondrial assay procedure discriminated clinically identified patients with primary biliary cirrhosis from normal subjects with a sensitivity of 83% and a specificity of 100%. This method compared favourably against a commercial ELISA method which had a sensitivity of 73% and a specificity of 100%. The automated enzymatic mitochondrial antibody assay is a high throughput assay of use for the routine diagnosis of patients with primary biliary cirrhosis with autoantibodies to the E2 subunit of the pyruvate dehydrogenase complex. The method is of potential value for economical and rapid screening to detect asymptomatic primary biliary cirrhosis in the at-risk segment of the population, namely middle aged women.

Conformational epitopes on the diabetes autoantigen GAD65 identified by peptide phage display and molecular modeling.

The major diabetes autoantigen, glutamic acid decarboxylase (GAD65), contains a region of sequence similarity, including six identical residues PEVKEK, to the P2C protein of coxsackie B virus, suggesting that cross-reactivity between coxsackie B virus and GAD65 can initiate autoimmune diabetes. We used the human islet cell mAbs MICA3 and MICA4 to identify the Ab epitopes of GAD65 by screening phage-displayed random peptide libraries. The identified peptide sequences could be mapped to a homology model of the pyridoxal phosphate (PLP) binding domain of GAD65. For MICA3, a surface loop containing the sequence PEVKEK and two adjacent exposed helixes were identified in the PLP binding domain as well as a region of the C terminus of GAD65 that has previously been identified as critical for MICA3 binding. To confirm that the loop containing the PEVKEK sequence contributes to the MICA3 epitope, this loop was deleted by mutagenesis. This reduced binding of MICA3 by 70%. Peptide sequences selected using MICA4 were rich in basic or hydroxyl-containing amino acids, and the surface of the GAD65 PLP-binding domain surrounding Lys358, which is known to be critical for MICA4 binding, was likewise rich in these amino acids. Also, the two phage most reactive with MICA4 encoded the motif VALxG, and the reverse of this sequence, LAV, was located in this same region. Thus, we have defined the MICA3 and MICA4 epitopes on GAD65 using the combination of phage display, molecular modeling, and mutagenesis and have provided compelling evidence for the involvement of the PEVKEK loop in the MICA3 epitope.

Characterization of epitopes for virus-neutralizing monoclonal antibodies to Ross River virus E2 using phage-displayed random peptide libraries.

Ross River virus (RRV) is the predominant cause of epidemic polyarthritis in Australia, yet the antigenic determinants are not well defined. We aimed to characterize epitope(s) on RRV-E2 for a panel of monoclonal antibodies (MAbs) that recognize overlapping conformational epitopes on the E2 envelope protein of RRV and that neutralize virus infection of cells in vitro. Phage-displayed random peptide libraries were probed with the MAbs T1E7, NB3C4, and T10C9 using solution-phase and solid-phase biopanning methods. The peptides VSIFPPA and KTAISPT were selected 15 and 6 times, respectively, by all three of the MAbs using solution-phase biopanning. The peptide LRLPPAP was selected 8 times by NB3C4 using solid-phase biopanning; this peptide shares a trio of amino acids with the peptide VSIFPPA. Phage that expressed the peptides VSIFPPA and LRLPPAP were reactive with T1E7 and/or NB3C4, and phage that expressed the peptides VSIFPPA, LRLPPAP, and KTAISPT partially inhibited the reactivity of T1E7 with RRV. The selected peptides resemble regions of RRV-E2 adjacent to sites mutated in neutralization escape variants of RRV derived by culture in the presence of these MAbs (E2 210-219 and 238-245) and an additional region of E2 172-182. Together these sites represent a conformational epitope of E2 that is informative of cellular contact sites on RRV.

Sex-determining region Y-related protein SOX13 is a diabetes autoantigen expressed in pancreatic islets.

The SOX (sex-determining region [SRY]-type high mobility group [HMG] box) family of transcription factors play key roles in determining cell fate during organ development. In this study, we have identified a new human SOX gene, SOX13, as encoding the type 1 diabetes autoantigen, islet cell antigen 12 (ICA12). Sequence analysis showed that SOX13 belongs to the class D subgroup of SOX transcription factors, which contain a leucine zipper motif and a region rich in glutamine. SOX13 autoantibodies occurred at a significantly higher frequency among 188 people with type 1 diabetes (18%) than among 88 with type 2 diabetes (6%) or 175 healthy control subjects (4%). Deletion mapping of the antibody epitopes showed that the autoantibodies were primarily directed against an epitope requiring the majority of the protein. SOX13 RNA was detected in most human tissues, with the highest levels in the pancreas, placenta, and kidney. Immunohistochemistry on sections of human pancreas identified SOX13 in the islets of Langerhans, where staining was mostly cytoplasmic. In mouse pancreas, Sox13 was present in the nucleus and cytoplasm of beta-cells as well as other islet cell types. Recombinant SOX13 protein bound to the SOX consensus DNA motif AACAAT, and binding was inhibited by homodimer formation. These observations-along with the known molecular interactions of the closely related protein, rainbow trout Sox23-suggest that SOX13 may be activated for nuclear import and DNA binding through heterodimer formation. In conclusion, we have identified ICA12 as the putative transcription factor SOX13 and demonstrated an increased frequency of autoantibody reactivity in sera from type 1 diabetic subjects compared with type 2 diabetic and healthy control subjects.

Young Chinese adults with new onset of diabetic ketoacidosis--clinical course, autoimmune status and progression of pancreatic beta-cell function.

AIMS: To examine the clinical course, autoimmune status and pancreatic beta cell function, over a 2-year period, in young Chinese subjects newly presenting with diabetic ketoacidosis (DKA). METHODS: A prospective study involving 562 out of 27,893 patients who were admitted to the medical ward with a principal diagnosis of diabetes mellitus during the recruitment period of 1 year. RESULTS: Of these 562 patients, 27 were aged less than 35 years and admitted with a diagnosis of DKA and 11 (six males and five females) of these were newly diagnosed. Antibodies to glutamic acid decarboxylase (GAD) were present in five patients. Anti-ICA 512 was not detected in any of the patients. Basal and post-glucagon stimulated plasma C-peptide remained in the insulin-deficient range although showing improvement at 2 years. CONCLUSIONS: These findings confirm the relative rarity of autoimmune Type 1 diabetes in young Chinese. Even when the clinical presentation takes the extreme form of acute DKA, less than 50% have positive autoimmune markers.

Primary biliary cirrhosis: an orchestrated immune response against epithelial cells.

Primary biliary cirrhosis (PBC) is an organ-specific autoimmune disease that predominantly affects women and is characterized by chronic progressive destruction of small intrahepatic bile ducts with portal inflammation and ultimately fibrosis. The serologic hallmark of PBC is the presence of antibodies to mitochondria, especially to the E2 component of the pyruvate dehydrogenase complex. The mechanisms by which (and if) such antibodies produce liver tissue injury are unknown. However, the presence of these antibodies has allowed detailed immunological definition of the antigenic epitopes, the nature of reactive autoantibodies and the characterization of T-cell responses. Several mechanisms may now be proposed regarding the immune-mediated bile duct damage in PBC, including the possible role of T-cell-mediated cytotoxicity and intracellular interaction between the IgA class of antimitochondrial antibodies and mitochondrial autoantigens. There are major questions which remain unanswered, including, of course, etiology, but also the reasons for female predominance, the absence of PBC in children, the relative ineffectiveness of immunosuppressive drugs, and the specific role of mitochondrial antigens. The data so far provide suggestive evidence that PBC is a mucosal disease; this thesis provides a basis for discussion of etiology via the enterohepatic circulation of toxins and/or infection.

The peculiar autoimmunity of primary biliary cirrhosis.

Autoantibodies to mitochondria (AMA, anti-M2) are a serologic hallmark of primary biliary cirrhosis (PBC). These react with three structurally and functionally related multienzymic complexes, the 2-oxoacid dehydrogenase complexes, but chiefly with the E2 subunit of pyruvate dehydrogenase complex (PDC-E2). Their very dose (95%) and specific association with PBC underpins the autoimmune concept of pathogenesis of that disease, notwithstanding several non-congruent features. Detailed studies, including structural analysis of epitopes, do not disclose how these autoantibodies originate. Their ubiquity in PBC has overshadowed the existence of a second set of relatively PBC-specific autoantibodies to nuclear antigens for which reactants have been cloned and characterized. These include centromeric proteins; proteins of the nuclear pore complex; nuclear dot proteins, which include Sp-100 and the promyelocytic leukemia antigen; and a recently identified autoantigen, SOX13. Certain of these reactants are DNA-binding proteins with transcriptional regulatory activity. Thus serum from individuals with the same clinical syndrome can have autoimmune reactivity to disparate mitochondrial and nuclear constituents in different cellular compartments. Antibody probing of phage displayed random peptide libraries, together with epitope scanning using overlapping sequential octameric peptides from the PDC-E2 sequence, showed that the discontinuous motifs MH, FV(E) and SYP contributed to a predicted conformational antibody epitope in the inner lipoyl domain of PDC-E2.

Monoclonal antibody screening of a phage-displayed random peptide library reveals mimotopes of chemokine receptor CCR5: implications for the tertiary structure of the receptor and for an N-terminal binding site for HIV-1 gp120.

The chemokine receptor CCR5 contains seven transmembrane-spanning domains. It binds chemokines and acts as co-receptor for macrophage (m)-tropic (or R5) strains of HIV-1. Monoclonal antibodies (mAb) to CCR5, 3A9 and 5C7, were used for biopanning a nonapeptide cysteine (C)-constrained phage-displayed random peptide library to ascertain contact residues and define tertiary structures of possible epitopes on CCR5. Reactivity of antibodies with phagotopes was established by enzyme-linked immunosorbent assay (ELISA). mAb 3A9 identified a phagotope C-HASIYDFGS-C (3A9 / 1), and 5C7 most frequently identified C-PHWLRDLRV-C (5C7 / 1). Corresponding peptides were synthesized. Phagotopes and synthetic peptides reacted in ELISA with corresponding antibodies and synthetic peptides inhibited antibody binding to the phagotopes. Reactivity by immunofluorescence of 3A9 with CCR5 was strongly inhibited by the corresponding peptide. Both mAb 3A9 and 5C7 reacted similarly with phagotopes and the corresponding peptide selected by the alternative mAb. The sequences of peptide inserts of phagotopes could be aligned as mimotopes of the sequence of CCR5. For phage 3A9 / 1, the motif SIYD aligned to residues at the N terminus and FG to residues on the first extracellular loop; for 5C7 / 1, residues at the N terminus, first extracellular loop, and possibly the third extracellular loop could be aligned and so would contribute to the mimotope. The synthetic peptides corresponding to the isolated phagotopes showed a CD4-dependent reactivity with gp120 of a primary, m-tropic HIV-1 isolate. Thus reactivity of antibodies raised to CCR5 against phage-displayed peptides defined mimotopes that reflect binding sites for these antibodies and reveal a part of the gp120 binding sites on CCR5.

Prediction of the immunodominant epitope of the pyruvate dehydrogenase complex E2 in primary biliary cirrhosis using phage display.

Primary biliary cirrhosis (PBC) is an autoimmune liver disease characterized by autoantibodies reactive with the pyruvate dehydrogenase complex. A conformational epitope has been mapped to aa 91-227 within the inner lipoyl domain of the E2 subunit (pyruvate dehydrogenase complex E2 (PDC-E2)). We have used phage display to further localize this epitope. A random heptapeptide library was screened using IgG from two patients with PBC, with negative selection using pooled normal IgG. Phage that contained peptide inserts (phagotopes) selected using PBC sera differed from those selected using IgG from patients with RA or polychondritis. Two motifs occurred only among the PBC-selected phagotopes; these were MH (13 sequences, 16 phagotopes) and FV (FVEHTRW, FVEIYSP, FVLPWRI). The phagotopes selected were tested for reactivity with anti-PDC-E2 affinity purified from four patients with PBC. Phagotopes that contained 1 of 15 different peptide sequences were reactive with one or more of these four anti-PDC-E2 preparations, whereas phagotopes that contained 1of the remaining 28 sequences were negative. The peptides (FVLPWRI, MHLNTPP, MHLTQSP) encoded by three phagotopes that were strongly reactive with all four preparations of anti-PDC-E2 were synthesized. Each of the selected peptides, but not an irrelevant peptide, inhibited the reactivity by ELISA of PBC serum with recombinant PDC-E2 and reduced the inhibition of the enzyme activity of PDC by a PBC serum. The peptide sequences, along with the known NMR structure of the inner lipoyl domain of PDC-E2, allow the prediction of nonsequential residues 131HM132 and 178FEV180 that contribute to a conformational epitope.

Enzyme inhibitory antibody to pyruvate dehydrogenase: diagnostic utility in primary biliary cirrhosis.

In primary biliary cirrhosis, autoantibodies are produced to the family of 2-oxoacid dehydrogenase complexes. These 'anti-mitochondrial' antibodies are traditionally detected by immunofluorescence but this method of detection is subjective and labour-intensive. We assessed an enzymatic mitochondrial antibody (EMA) assay based on antibody inhibition of enzymatic activity of pyruvate dehydrogenase complex in wells of microtitre plates with a colorimetric read-out. We tested 48 Australian and 1947 Japanese patients with primary biliary cirrhosis, 306 normal subjects and 691 patients with various hepatic and non-hepatic diseases. The overall sensitivity of the EMA for the diagnosis of primary biliary cirrhosis, 82%, was slightly lower than that of immunofluorescence, 90% The advantages of the EMA test include high specificity, >99%, and semi-automated features facilitating objectivity, rapidity, simplicity and economy. The EMA test could be particularly applicable to population screening for early primary biliary cirrhosis.