Phenotyping and auto-antibody production by liver-infiltrating B cells in primary sclerosing cholangitis and primary biliary cholangitis

Abstract

Primary biliary cholangitis (PBC) and primary sclerosing cholangitis (PSC) are immune-mediated biliary diseases that demonstrate prominent and restricted genetic association with human leukocyte antigen (HLA) alleles. In PBC, anti-mitochondrial antibodies (AMA) are specific and used as diagnostic biomarkers. PSC-relevant auto-antibodies remain controversial despite a distinct HLA association that mirrors archetypical auto-antigen driven disorders. Herein, we compared antibody-secreting B cells (ASCs) in PSC and PBC liver explants to determine if liver-infiltrating ASCs represent an opportune and novel source of disease-relevant auto-antibodies. Using enzymatic digestion and mechanical disruption, liver mononuclear cells (LIMCs) were isolated from fresh PSC and PBC explants and plasmablast (CD19+CD27+CD38^hiCD138-) and plasma cell (CD19+CD27+CD38^hiCD138+) ASCs were enumerated by flow cytometry. We observed 45-fold fewer plasma cells in PSC explants (n = 9) compared to PBC samples (n = 5, p < 0.01) and 10-fold fewer IgA-, IgG- and IgM-positive ASCs (p < 0.05). Liver-infiltrating ASCs from PSC and PBC explants were functional and produced similar concentrations of IgA, IgG and IgM following 2 weeks of culture. Antibody production by PBC ASCs (n = 3) was disease-specific as AMA to pyruvate dehydrogenase complex E2 subunit (PDC-E2) was detected by immunostaining, immunoblotting and ELISA. Antibody profiling of PSC supernatants (n = 9) using full-length recombinant human protein arrays (Cambridge Protein Arrays) revealed reactivities to nucleolar protein 3 (5/9) and hematopoietic cell-specific Lyn substrate 1 (3/9). Array analysis of PBC supernatants (n = 3) detected reactivities to PDC-E2 and hexokinase 1 (3/3). In conclusion, we detected unique frequencies of liver-infiltrating ASCs in PSC and PBC and in so doing, highlight a feasible approach for understanding disease-relevant antibodies in PSC.

Keywords: Antibody-secreting B cells; Auto-antibodies; Autoimmunity; Biomarkers; Primary biliary cholangitis; Primary sclerosing cholangitis; Protein arrays.