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

Abstract

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)

Differential epitope mapping of antibodies to PDC-E2 in patients with hematologic malignancies after allogeneic hematopoietic stem cell transplantation and primary biliary cirrhosis

“…30 Moreover, the antibody response in hemato-oncologic patients was directed exclusively against PDC-E2 with no reactivity toward OGDC or BCOADC, the other immunogenic reactants identified in PBC. Differences were also confirmed analyzing the involved IgG subclasses, confirming the previously described prevalence of IgG3 in PBC 20,21 and prevalently detecting IgG1 and IgG2 in patients after DLI arguing in favor of a potentially T-cell-dependent immunoglobulin production. 31,32 Most importantly, the absence of detectable liver disease in all of the examined patients over time furthermore distinguishes the population, although a delayed onset of a potential liver disease cannot be excluded considering the presence of AMAs for years in otherwise asymptomatic patients who eventually develop PBC.…”

Immunization of experimental animals with dihydrolipoamide acetyltransferase, as a purified recombinant polypeptide, generates mitochondrial antibodies but not primary biliary cirrhosis

“…PDH was used as the coating antigen in the ELISA assay using techniques described elsewhere (15,16). Polystyrene microtiter plates were coated with 2 Fg per ml PDH in carbonate coating buffer overnight at 4°C.…”

PBC and AMA?what is the connection?

“…That AMA are primarily of the IgG3 and IgM isotype is also consistent with a viral infection. 54 We reported the presence of virus-like particles in the supernatants of isolated biliary epithelial cells in vitro, but until molecular characterization and specificity can be shown, any conclusions must remain speculative.…”

“…54 • Analysis of the immunoglobulin gene mutations of a panel of monoclonal anti-PDC-E2 derived from humans with PBC suggests an antigen-driven selection of high-affinity antibodies, hinting at the persistence of a foreign antigen. 55 Similar conclusions have been drawn from the analysis of T-cell receptor V␤ usage by liver infiltrating T cells from explanted PBC livers.…”