Keratin 19 and mesenchymal markers for evaluation of epithelial-mesenchymal transition and stem cell niche components in primary biliary cholangitis by sequential elution-stripping multiplex immunohistochemistry.

Multiplexed immunohistochemical techniques give insight into contextual cellular relationships by offering the ability to collect cell-specific data with spatial information from formalin-fixed, paraffin-embedded tissue sections. We established an automated sequential elution-stripping multiplex immunohistochemical assay to address two controversial scientific questions in the field of hepatopathology: 1) whether epithelial-to-mesenchymal transition or mesenchymal-to-epithelial transition occurs during liver injury and repair of a chronic liver disease and 2) if there is a stromal:epithelial relationship along the canals of Hering that would support the concept of this biliary structure being a stem/progenitor cell niche. Our 4-plex assay includes both epithelial and mesenchymal clinical immunohistochemical markers and was performed on clinical human liver specimens in patients with primary biliary cholangitis. The assay demonstrated that in each specimen, co-expression of epithelial and mesenchymal markers was observed in extraportal cholangiocytes. In regard to possible mesenchymal components in a stem cell niche, 82.3% ± 5.5% of extraportal cholangiocytes were intimately associated with a vimentin-positive cell. Co-expression of epithelial and mesenchymal markers by extraportal cholangiocytes is evidence for epithelial to mesenchymal transition in primary biliary cholangitis. Vimentin-positive stromal cells are frequently juxtaposed to extraportal cholangiocytes, supporting an epithelial:mesenchymal relationship within the hepatobiliary stem cell niche. Our automated sequential elution-stripping multiplex immunohistochemical assay is a cost-effective multiplexing technique that can be readily applied to a small series of clinical pathology samples in order to answer scientific questions involving cell:cell relationships and cellular antibody expression.