IgG4 Levels in Bile for Distinguishing IgG4-Associated Cholangiopathy from Other Biliary Disorders: A Single Blinded Pilot Study

Review of primary sclerosing cholangitis with increased IgG4 levels

Primary sclerosing cholangitis (PSC) is a chronic progressive liver disease. Sub-types of PSC have been described, most recently PSC with elevated serum and/or tissue IgG4 subclass. We aim to summarise the clinical phenotype, disease associations, differential diagnosis, response to therapy and pathogenic mechanisms underlying PSC-high IgG4 subtype. We reviewed PubMed, MEDLINE and Embase with the search terms "primary sclerosing cholangitis", "IgG4", and "IgG4-related sclerosing cholangitis (IgG4-SC)". Elevated serum IgG4 are found in up-to one-quarter, and abundant IgG4-plasma cell infiltrates in the liver and bile ducts are found in up-to one-fifth of PSC patients. This group have a distinct clinical phenotype, with some studies reporting a more aggressive course of liver and associated inflammatory bowel disease, compared to PSC-normal IgG4 and the disease mimic IgG4-SC. Distinguishing PSC-high IgG4 from IgG4-SC remains challenging, requiring careful assessment of clinical features, organ involvement and tissue morphology. Calculation of serum IgG4:IgG1 ratios and use of a novel IgG4:IgG RNA ratio have been reported to have excellent specificity to distinguish IgG4-SC and PSC-high IgG4 but require validation in larger cohorts. A role for corticosteroid therapy in PSC-high IgG4 remains unanswered, with concerns of increased toxicity and lack of outcome data. The immunological drivers underlying prominent IgG4 antibodies in PSC are incompletely defined. An association with PSC-high IgG4 and HLA class-II haplotypes (B*07, DRB1*15), T-helper2 and T-regulatory cytokines (IL4, IL10, IL13) and chemokines (CCL1, CCR8) have been described. PSC-high IgG4 have a distinct clinical phenotype and need careful discrimination from IgG4-SC, although response to immunosuppressive treatments and long-term outcome remains unresolved. The presence of IgG4 likely represents chronic activation to persistent antigenic exposure in genetically predisposed individuals.

Immunoglobulin G4-related cholangiopathy: clinical and experimental insights

PURPOSE OF REVIEW

The clinical spectrum of immunoglobulin G4-related disease (IgG4-RD) is diverse and the disease may affect multiple organ systems. The pancreatobiliary tract probably is the clinically most important localization of the disease but diagnosing IgG4-related cholangiopathy (synonym: IgG4-associated cholangitis) or autoimmune pancreatitis is often challenging. This review summarizes the current best practice in diagnosing and treating IgG4-related cholangiopathy and recent advances in our understanding of its cause.

RECENT FINDINGS

The identification of IgG4-switched B-cell and plasma cell populations in patients with IgG4-related cholangiopathy and IgG4-RD and their disappearance upon successful treatment have established the role of these cells in the disorder. Ultimately, these findings may lead to the development of more sensitive diagnostic tests. The observation that many of the predominantly 50-70 years old male patients have been exposed lengthily to occupational hazardous compounds further supports the idea that chronic antigenic stimulation may be a pivotal etiological aspect of the disease. Immunosuppressive treatment remains the therapeutic cornerstone in IgG4-RD.

SUMMARY

Currently available experimental evidence classifies IgG4-RD as an immune-mediated disorder, providing support to the use of immunosuppressants and possibly even more specific therapies targeting the B-cell and plasma cell lineages.