Immune complexes in primary biliary cirrhosis contain mitochondrial antigens

Primary biliary cirrhosis and primary sclerosing cholangitis

Primary biliary cirrhosis and primary sclerosing cholangitis are the most common chronic cholestatic liver diseases in adults that lead to biliary cirrhosis and its inherent complications such as portal hypertension and liver failure. Although important advances in the understanding of the pathogenesis of these conditions have been accomplished in the last two decades, much work is needed to uncover the interaction of genetic and immunologic mechanisms involved in their pathogenesis. Ursodeoxycholic acid at dosage of 13 to 15 mg/kg/d is the only agent that can currently be recommended in the treatment of PBC. No medical therapy aimed at disrupting disease progression is available for patients with primary sclerosing cholangitis, although several agents with different properties are currently under evaluation. Liver transplantation is the treatment of choice for patients with primary biliary cirrhosis and primary sclerosing cholangitis with end-stage liver disease.

The predominance of IgG3 and IgM isotype antimitochondrial autoantibodies against recombinant fused mitochondrial polypeptide in patients with primary biliary cirrhosis

Autoantibodies against inner mitochondrial membrane proteins are a hallmark of primary biliary cirrhosis. Specifically, these antimitochondrial autoantibodies recognize two polypeptides of approximately 70 and 52 kD, respectively. Although the specificity of antimitochondrial autoantibodies has been studied for the past 2 decades, the complementary DNA encoding the major primary biliary cirrhosis-specific 70 kD antigen has only recently been cloned. The availability of the recombinant autoantigen has resulted in the development of a highly sensitive and specific ELISA to detect antimitochondrial autoantibodies and to determine their immunoglobulin isotypes. We report herein that IgG3 is the predominant isotype of antimitochondrial autoantibodies in a group of 74 primary biliary cirrhosis patients. This finding is significant in light of the genomic immunoglobulin in heavy chain gene arrangement. Ninety-three per cent of primary biliary cirrhosis patients possessed IgG3 antimitochondrial autoantibodies with titers of 1:10(3) or higher; 32% of these patients possessed titers of 10(4), 29% at 10(5) and 7% at 10(6). IgM antimitochondrial autoantibodies were next most prevalent; 63% of the patients were positive and 50% of these patients showed titers of 10(3), 43% at 10(4) and 6% at 10(5). Other isotypes were present but in much lower titer and occurrence. Isotypes of antimitochondrial autoantibodies reactive to the 52 kD antigen were also determined using immunoblotting techniques. The predominance of IgG3 and IgM were similarly observed. Finally, the serum immunoglobulin isotype levels of primary biliary cirrhosis patients were compared with healthy normal adults by radial immunodiffusion. Serum IgG3 and IgM were very elevated in primary biliary cirrhosis; with IgG3 at 5.5-fold and IgM at 4.3-fold above normals.(ABSTRACT TRUNCATED AT 250 WORDS)

Immunology of primary biliary cirrhosis

(1) The serological diagnosis of PBC is possible in almost 100% of cases when appropriate methods and specific antigen preparations are used such as the purified ATPase fraction by ELISA for the detection of anti-M2, sonicated mitochondria by immunodiffusion for the demonstration of precipitating antibodies against M-A or M-B, and cell cultures by immunofluorescence for the detection of antibodies against nuclear dots. (2) The establishment of AMA profiles obtained by ELISA and CFT seems to be a sensitive approach to a better definition of the natural course of PBC. A distinction between a rather benign and a more progressive course seems especially possible in the presence of the AMA profiles A and B (anti-M9 and/or anti-M2-positive only by ELISA) versus D (anti-M2-, anti-M4-, anti-M8-positive in the CFT). (3) The analysis of cellular immune reactions in vitro and in vivo suggests an activation of cytotoxic T cells as well as a defect in the function of T suppressor cells. (4) Although the aetiology of PBC is unknown, the detection of MHC Class II antigens on bile duct epithelial cells in liver biopsies of patients with PBC but not of normal individuals may imply that an infectious agent being exposed in association with these MHC structures may trigger the disease. The inability of the immune system in controlling this infectious process would then lead to an ongoing inflammatory reaction which is responsible for the continuous destruction of bile ducts within portal triads.

Nature of immune complexes in autoimmune chronic active hepatitis

Immune complexes containing antinuclear antibodies have been observed in autoimmune chronic active hepatitis. Using a library of nuclear constituents (deoxyribonucleic acid, small nuclear ribonucleoproteins, and histones), we analyzed the antigens involved in formation of immune complexes. Immune complexes were defined in dissociation experiments, and after separation under dissociating conditions. Immune complexes composed of histones and immunoglobulin G were observed in four of nine immune complex-positive autoimmune chronic active hepatitis sera. Immune complexes containing the small nuclear ribonucleoprotein U1-RNP and immunoglobulin G were observed in two additional samples. Kidney eluates obtained from 2 patients with autoimmune chronic active hepatitis and membranous glomerulonephritis revealed enrichment of anti-U1-RNP, suggesting specific deposition of this antibody in complexed form. Circulating immune complexes containing histones were observed only in patients with autoimmune chronic active hepatitis-associated sicca syndrome; those containing U1-RNP were restricted to patients with autoimmune chronic active hepatitis associated with kidney disease.

Demonstration of immune complexes containing the ribonucleoprotein antigen Ro in primary biliary cirrhosis

We have previously demonstrated circulating and tissue-fixed immune complexes containing the small cytoplasmic ribonucleoprotein antigen Ro and immunoglobulin G (IgG) in a case of sicca syndrome associated with primary biliary cirrhosis. To establish the overall prevalence of such complexes in liver disease, we performed dissociation experiments under conditions of Ro antigen excess. Of the diseases tested, Ro-containing immune complexes were restricted to cases with primary biliary cirrhosis. Sera from 29 of the 47 patients with primary biliary cirrhosis (60%) showed IgG-containing immune complexes; 10 of the 29 sera samples (34%) positive for IgG-containing immune complexes exhibited immune complexes composed of Ro and anti-Ro IgG. These complexes sedimented predominantly as intermediate or large aggregates and were encountered most frequently in cases with extra-hepatic features.

Effects of penicillamine on serum immunoglobulins and immune complex-reactive material in primary biliary cirrhosis

Although penicillamine is used in the treatment of primary biliary cirrhosis, its mechanism of action in this disease is unknown. As an immunologic action had been attributed to the drug, we investigated whether penicillamine might alter serum immunoglobulin levels or immune complex-reactive material in patients with primary biliary cirrhosis. Immunoglobulin levels and immune complex reactivity were measured and clinical tests were performed in 53 consecutive patients entering a double-blind randomized trial of 750 mg vs. 250 mg of penicillamine. Measurement of immune complex reactivity was determined by laser nephelometry, 125I-C1q binding, and Raji cell assays. Immune complex reactivity was detected by at least one assay in 75% of patients tested before treatment. Sixty-two percent were positive in the C1q assay, 28% in the Raji cell assay, and 39% by nephelometry. After therapy with either dose, we found no change in immune complex-reactive material by any assay. Concentrations of immunoglobulins G and M fell (p less than 0.05) after 12 mo of therapy. Concentrations of immunoglobulin A decreased (p less than 0.05) only in the high-dose group. Correlation was not consistent between results of immune complex assays and clinical liver tests. Although immunoglobulin levels fell during penicillamine therapy, no decrease in immune complex-reactive material was detected. The effect of penicillamine in primary biliary cirrhosis is not mediated through alteration of immune complex-reactive material.