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

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 (CD19þCD27þCD38hiCD138) and plasma cell (CD19þCD27þCD38hiCD138þ) ASCs were enumerated by flow cytometry. We observed 45-fold fewer plasma cells in PSC explants (n ¼ 9) compared to PBC samples (n ¼ 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 ¼ 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 ¼ 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 ¼ 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.