CD4 and cholangiocarcinoma: Serum cytokine profiles, lymphocyte subpopulations (B lymphocytes, CD8+ cytotoxic T lymphocytes, CD4+ T-helper lymphocytes, and NK cells), and cytotoxic activity of PBMCs against the cholangiocarcinoma cell line CL-6 were evaluated using cytometric bead array (CBA) with flow cytometry analysis.