Cytokeratin Detection in Lymphoid Tumor Cell Lines: Implications for Flow Cytometry and Molecular Analyses

Cytokeratins are widely used as epithelial markers in diagnostic pathology and flow cytometry, and malignant lymphomas are generally considered cytokeratin-negative except for undifferentiated large cell lymphomas. During antibody screening experiments using flow cytometry, intracellular cytokeratin signals were unexpectedly detected in cultured lymphoma cell lines after cell permeabilization. Although cytokeratin is a component of the cytoskeleton, this finding raised concerns regarding the interpretation of cytokeratin positivity in lymphoid cells. To elucidate the nature of cytokeratin detection in lymphomas, cultured T-cell, B-cell, and natural killer cell lymphoma lines were analyzed using immunohistochemistry, flow cytometry, and quantitative RT-PCR (qRT-PCR), with epithelial carcinoma cell lines and keratin-free cells as references. Because malignant lymphomas disseminate systemically, we examined whether this behavior was associated with epithelial-mesenchymal transition-like features. Cytokeratins were not detected on the cell surface of lymphoid or epithelial cells but were detected intracellularly in multiple lymphoma cell lines. qRT-PCR confirmed the expression of multiple keratin transcripts in lymphoid cells, without correlation with epithelial-mesenchymal transition-related markers, including CDH1. These findings indicate that intracellular cytokeratin detection can occur in lymphoma cell lines without evidence of epithelial differentiation or association with EMT-related markers and should be considered when interpreting cytokeratin positivity.