T cell responses to ursodeoxycholic acid and antibody profiles in primary biliary cholangitis

Gray, Kathryn (2018) T cell responses to ursodeoxycholic acid and antibody profiles in primary biliary cholangitis. Doctoral thesis, Northumbria University.

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Abstract

Primary Biliary Cholangitis (PBC), formerly ‘Primary Biliary Cirrhosis’, is an autoimmune disease of the interhepatic bile ducts. Their damage leads to bile retention in the liver and subsequent damage to hepatocytes, leading to perpetuating injury and tissue damage, causing destruction of the normal liver architecture and eventual cirrhosis.

The current therapy given to PBC patients, ursodeoxycholic acid (UDCA), is insufficient to prevent disease progression, and appears to only slow the natural history of the disease. Additionally, the drug is only effective in around 80% of patients with the remaining 20% showing no apparent benefit after a year of use. Breakthrough studies appear to suggest that there may be differences in clinical biochemical parameters between these patient groups which may explain their marked differences in response to the drug. These findings are leading to PBC being considered as an umbrella term encompassing two- or more separate disease subsets, broadly ‘responders’ and ‘non-responders’ referring to response to UDCA, with ‘non-responder’ categorisation requiring the inability of the drug to significantly lower a patient’s blood AST, ALP and bilirubin levels during the given time frame. Further elucidation of these subsets is crucial to identify patients and potentially allow the development of differential therapies which may benefit these “nonresponders”.

The mechanism of action of UDCA has been investigated in this thesis with the aim to use this data to highlight key pathways of interest differentiating the responder/non-responder subgroups. This involved flow cytometric analysis and ELISpot analysis of the effect of UDCA on T cells and also xCELLigence and supernatant transfer assays to investigate an impact on the cholangiocytes. Further elucidation of the responder/non-responder subgroups came from comparing antibody profiles of these groups. Multiple indirect enzyme-linked immunosorbent assays (ELISAs) were carried out to measure antibody titre and therefore detect patterns of auto-antibody isotypes in serum from PBC patients known to be “responders” (62) or “non-responders” (15) to UDCA. Recombinant human PBC autoantigens E2, E2 inner lipoyl domain (E2ILD) and E3 binding protein (E3BP) were used to uncover statistically significant differences in antibody responses. Using cross-sectional analysis, it was found that results from patient data were able to replicate the proposed responder and non-responder grouping based on age and liver function criteria. It was found that compared to responders, non-responders have higher levels of anti-E2 IgE (p=0.025), anti-E2ILD IgA (p=0.047) and anti-E2ILD IgG3 (p=0.01). The study also found that men with PBC, generally considered non-responders, have significantly lower levels of some antibodies, which are higher in non-responders, anti-E2IgE (p=0.003) and anti-E2ILD IgG3 (p=0.05). This is further evidence that men with PBC may constitute their own sub group of non-responders.

These findings provide further evidence that the disease includes biologically different subsets which should be treated differently. Differences in antibody isotype to dominant autoantigens suggests that there may be significant functional differences in T helper cell subsets in each patient group. Further investigation into the differences between these subsets could provide a diagnostic tool which could be used early on in diagnosis to categorise patients for stratified treatment.

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