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Occasional Viewpoint PBC: an Infectious Disease?

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Occasional Viewpoint PBC: an Infectious Disease? 586 Gut 2000;47:586–588 Occasional viewpoint Gut: first published as 10.1136/gut.47.4.586 on 1 October 2000. Downloaded from PBC: an infectious disease? Primary biliary cirrhosis (PBC) is characterised by community only 19 per million.10 Similarly, while PBC is progressive destruction of the middle sized intrahepatic almost absent in India, the prevalence of end stage PBC ducts, leading to liver failure and, in the absence of trans- among first generation migrants to the UK from the Indian plantation, death. While ursodeoxycholic acid may slow subcontinent is 14 per million.11 progression, there is as yet no curative therapy. As the pathogenesis of PBC is unknown, it is diYcult to develop a Clustering logical therapeutic strategy. PBC has been considered an Cases of PBC tend to “cluster” within areas. This autoimmune disease although immunosuppressive therapy phenomenon was first described in SheYeld where cases of is relatively ineVective; here we discuss the possibility that PBC clustered in one area supplied by the Rivelin there may be an infectious aetiology. reservoir; the point prevalence here was 115 per million compared with 13 per million elsewhere in SheYeld.12 A Autoimmune features of PBC subsequent study by Chetwynd showed significant evi- There are clear autoimmune aspects to PBC: there is a dence of spatial clustering13; this clustering was unrelated strong association with extrahepatic autoimmune diseases to urban or rural location or to diagnostic activity, suggest- such as thyroid disease. Overlap syndromes between PBC ing a true clustering eVect. and autoimmune hepatitis have been well documented12 although the response to immunosuppression is at best GENETIC poor. One of the characteristic features of PBC is the There is a marked familial component to PBC, there is only association with disease specific autoantibodies: these a weak HLA association (with B8), and there is no 14–18 include not only the antimitochondrial antibodies (AMA) childhood equivalent. The sibling relative risk of PBC 8 but also antibodies to components of the nuclear pore (ës) (10.5) is similar to that for rheumatoid arthritis and 15 complex (such as gp210). The antigens recognised by less than that for diabetes or systemic lupus 19 20 AMA have been identified (PDC-E2; OGDC-E2; E3BP; erythematosus. When two members are aVected, the PDC-E1á; BCOADC-E2) and are located on the inner disease tends to occur at the same time rather than at the aspect of the mitochondrial membrane.3–7 same age, compatible with an external trigger. THE TRANSPLANTATION MODEL AMA AND PBC AMA may precede the clinical, biochemical, and histologi- PBC specific autoantibodies (AMA and gp210) persist http://gut.bmj.com/ cal features of PBC, suggesting that these antibodies may after transplantation in all subjects and histological evidence of recurrence is demonstrated in up to 20% of have a pathological role. However, these antigens are 20 neither organ nor disease specific. Why the biliary epithe- patients by 10 years. Within these grafts, aberrant distri- bution of E2, typical of PBC, occurs whether or not there lial cells are the main targets of disease may be explained by 21 the observation that in PBC, but not other liver diseases is histological evidence of recurrence. Furthermore, both and normal liver, biliary epithelial cells have E2 present on the risk and rate of recurrence after liver transplantation is related to increased immunosuppression.22 This situation is their plasma membrane. Several groups have attempted to on September 29, 2021 by guest. Protected copyright. generate animal models of PBC by immunising animals analogous to the universal recurrence of chronic hepatitis with antigens recognised by AMA: injections of tissue or C virus infection in liver allografts following transplanta- tion, which again may be enhanced by high doses of recombinant mitochondrial antigens were given to murine 23 and other animal models, generating AMA but no bile duct immunosuppressive agents. This observation strongly lesions.8 More recently, Jones et al have suggested that suggests that some factor(s) in the host induces aberrant PBC-like bile duct lesions and AMA can be found in SJL E2 expression. mice, immunised with pyruvate dehydrogenase.9 There IN VIVO TRANSMISSION remains no clear evidence that AMA (or other PBC There is no evidence for PBC being transmitted sexually or specific autoantibodies) are linked to the pathogenesis of by blood transfusion. However, Hannan in a communica- the disease. tion to the British Association for the Study of the Liver (1999) described two babies born of mothers with PBC An infectious aetiology? who developed transient cholestatic liver disease associated There are several observations that suggest the possibility with the appearance of AMA. While the authors suggested that an infectious agent may result in PBC. that transplacental transmission of AMA could be the cause of the liver damage, an alternative explanation is that EPIDEMIOLOGICAL there is transplacental or perinatal transmission of an Prevalence studies and the eVect of migration infective agent. There is global variation in the reported prevalence of PBC and, although part of the variation in prevalence may reflect IN VITRO EVIDENCE FOR A TRANSMISSIBLE FACTOR methodological factors, there is likely to be a true variation in Biliary epithelial cells isolated from patients with PBC, but incidence. This is supported by studies examining the eVect not from patients with other liver diseases or normal sub- of migration: people migrating between diVerent geographi- jects, show both in vivo and in vitro E2 staining on plasma cal areas seem to take on the prevalence of the host popula- tion, thus in Britain, the prevalence is about 150–240 per Abbreviations used in this paper: PBC, primary biliary cirrhosis; million whereas among British immigrants to Australia the AMA, antimitochondrial antibodies; HIAP, human intracisternal prevalence is 47 per million and for the endemic Australian A-type peptide; UTI, urinary tract infection. www.gutjnl.com PBC: an infectious disease? 587 membranes. Macrophages in portal lymph nodes from prokaryocytes taken up by amoeboid cells; thus the struc- patients with PBC have increased staining by AMA. Biliary ture and function of mitochondria and aerobic bacteria are epithelial cells isolated from normal individuals incubated similar. R mutants diVer from wild-type enterobacteria Gut: first published as 10.1136/gut.47.4.586 on 1 October 2000. Downloaded from with homogenised lymph node from a patient with PBC mainly in the defective synthesis of the saccharide protein and then cultured for seven days develop E2 staining on of lipopolysaccharide.34 This results in the diVerent plasma. If supernatant from these “infected” epithelial cells molecular organisation of the cell membrane and the is incubated with normal biliary epithelial cells they too possibility that R mutants might possess diVerent charac- develop aberrant E2 staining on plasma membranes; this teristics, especially those related to immunogenic proper- eVect can be abolished by irradiation of the supernatant, ties. Phylogenetic conservation and wide prevalence of raising the possibility that there is a transmissible agent in bacterial and mitochondrial polypeptides suggests immune the PBC lymph nodes and supernatants.24 tolerance to antigen in humans. Immune tolerance may be terminated when polypeptides are presented in a strong Putative infectious agents immunogenic form or when a defect in the immune system MYCOBACTERIA occurs; for example, R forms of enterobacteria in the gut As granulomas, occurring either as aggregates of histio- may induce AMA in PBC patients. Again, this hypothesis cytes or non-caseating lesions adjacent to damaged bile linking E coli infection and PBC cannot be sustained as the ducts, are commonly found in PBC, it was suggested that association between recurrent UTI and PBC has not been mycobacteria have a role in the pathogenesis of PBC. An confirmed by all studies35 and AMA found in patients with initial study by Vilagut et al reported that all of 19 PBC sera UTI are of low titre and of diVerent specificity.36 Further- reacted with an extract from the atypical mycobacteria more, Tanaka et al were unable to find evidence of bacterial M gordonae; identical recognition profiles were produced or mycobacterial genomic products in livers from patients with two polypeptides of 70–65 and 55 kDa.25 There were with PBC.37 no other reactions with nine other atypical mycobacteria or with controls. Two main mitochondrial antigens identified VIRUSES by sera from PBC patients, PDH-E2 and BCKDH-E2, To date, no specific virus has been implicated in the patho- were also recognised by eluted antimycobacterial antibod- genesis of PBC. Following demonstration that human ies, indicating that there is cross reactivity of these anti-M intracisternal A-type peptide (HIAP) could be isolated gordonae antibodies with the mitochondrial antigen against from the salivary glands of patients with Sjogren’s which AMA react in PBC. The authors proposed that an syndrome,38 immunoblotting studies have indicated that induced humoral response to antigen from M gordonae may many patients with PBC have seroreactivity with retroviral evoke a sequence of autoreaction events resulting in the proteins (35% HIVp24; 51% HIAP).39 However, this pat- existence of AMA in genetically susceptible individuals. tern of seroreactivity is also seen in patients with primary Follow up studies concluded that antibody to
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