Sulphite oxidase (SO) - a mitochondrial autoantigen as target for humoral and cellular immune reactions in primary sclerosing cholangitis.

BACKGROUND: In a recent study we had evidence that sulphite oxidase (SO) may be a relevant autoantigen in primary sclerosing cholangitis (PSC). Aim of the present study was, therefore, to analyse humoral and cellular immune-reactivity towards SO in these patients in more detail. METHODS: Sera from 53 patients with PSC (30 untreated and 23 treated with ursodeoxycholic acid [UDCA] at time of analysis), from 422 patients with different hepatic and non-hepatic disorders, and from 50 healthy individuals were tested by ELISA for antibodies against full-length-SO (SO-fl) and its three major domains expressed in E.coli (SO-I, SO-II, SO-III). For epitope-mapping, 29 overlapping peptides were used. Peripheral blood mononuclear cells (PBMC) were obtained from 33 PSC-patients and analysed for SO-induced proliferation, production of cytokines, and expression of the activation marker cluster of differentiation (CD) 69. RESULTS: 43% of the 30 untreated and 26% of the 23 treated PSC-patients had IgG anti-SO-antibodies predominantly reacting with SO-fl, SO-I and SO-II. Antibody-reactivity decreased after UDCA-treatment. Prevalence and reactivity of anti-SO-antibodies were significantly higher in PSC than in patients with other hepatic and non-hepatic disorders. Epitope mapping revealed no distinct immuno-dominant regions within SO. Incubation of PBMC from PSC-patients (but not from controls) with SO-antigens revealed an activation of B-cells and a T-helper cell type-2 reaction pattern (production of interleukin [IL]-13, IL-10). CONCLUSIONS: PSC-patients show humoral and cellular immune response towards SO. Antibodies may be predominantly directed against conformational epitopes. SO enhances in vitro especially T-helper cell type-2 immune-reactions, which may be pro-fibrotic. SO is a detoxifying enzyme present also in bacteria; further studies analysing its role in the aetiology and pathogenesis in PSC may, therefore, be important.

Analysis of the clinical relevance of antimitochondrial antibodies to the ß- and γ-subunits of the F1F0-ATPase in patients with primary biliary cirrhosis.

BACKGROUND: In a recent study we showed that in patients with primary biliary cirrhosis (PBC) being positive or negative for anti-M2 antibodies reacting with the 2-oxoacid-dehydrogenase complex (ODC) also antibodies to the beta- and gamma-subunits of F1F0-ATPase (anti-ß, anti-γ) occur. This is a mitochondrial enzyme but parts are also expressed on plasma membranes of endothelial cells. Here we wanted to analyse in more detail their clinical relevance. METHODS: Fifty-nine untreated and histologically defined PBC patients who had been followed for at least five years were included into the study (51 anti-M2 positive, 8 anti-M2 negative). Twenty-three of them were treated in the follow up with ursodeoxycholic acid (UDCA), eight received during a trial methotrexate (MTX). In 13 patients orthotopic liver transplantation (OLT) had to be performed. Serum samples before and during therapy were available. Patients were analysed with respect to laboratory parameters, disease activity and histological stages.Patients' sera were tested by ELISA for IgG- and IgM-antibodies against the beta- and gamma-subunits which had been recombinant expressed in E.coli and highly purified by electro-elution from SDS-gels after electrophoresis. RESULTS: Fifty-nine percent of the anti-M2 positive and 50% of the anti-M2 negative PBC patients had anti-ß- and/or anti-γ-antibodies. There were no differences between anti-ß- and/or anti-γ-antibody positive or negative patients with respect to biochemical parameters, immunoglobulins, histological stages or disease activity. Antibody reactivity significantly decreased during UDCA and MTX-treatment and also after OLT. CONCLUSIONS: Antibodies to the ß- and γ-subunits of F1F0-ATPase occur in anti-M2 positive and -negative PBC but do not have any relevance with respect to clinical activity or prognosis. However, in contrast to the anti-M2 antibodies they decrease during UDCA and immunosuppressive therapy.

Identification of α-tubulin as an autoantigen recognized by sera from patients with neuropsychiatric systemic lupus erythematosus.

In a previous study we found in 50% of patients with neuropsychiatric manifestations of systemic lupus erythematosus (NP-SLE) organ specific antibodies to 45-56 kD proteins in a 100,000 g supernatant (SN) from bovine brain mitochondria. Aim of the present study was to identify the corresponding target antigen. A 100,000 g SN from bovine brain mitochondria was applied to SDS-gel electrophoresis. A 50 kD band recognized by sera from patients with NP-SLE in the Western blot (WB) was excised from the gels and applied to mass spectrometry. The identified protein was expressed in Escherichia coli and retested against sera from eleven patients with NP-SLE (severe symptoms n=6, mild symptoms n=5), 26 SLE-patients without NP manifestations and 53 controls (patients with multiple sclerosis, epilepsy, healthy blood donors). Mass spectrometry of the 50 kD band revealed the presence of α-tubulin. Applying the recombinant α-tubulin in the WB, four of the eleven NP-SLE patients (36%), one of the 26 patients with SLE without NP manifestations (4%) and none of the 53 controls reacted with α-tubulin. The antibodies were more frequently found in patients with severe (50%) than with mild NP-SLE (20%). α-tubulin may be a novel marker autoantigen for a neuropsychiatric manifestation at least in a subgroup of patients with SLE. Whether anti-α-tubulin antibodies are of pathogenetic relevance has still to be clarified.