['The present study was intended to assess transdifferentiation from tubular epithelial cells to macrophage- like cells.', 'Puromycin aminonucleoside nephrotic rats were sacrificed at days 4, 8, 24 and 112. We immunohistochemically evaluated CD68, CD163, and cytokeratin AE1/AE3, known as markers for macrophages and tubular epithelial cells. Nitrotyrosine, gp91(phox) and Rac 1 expressions was also analyzed. CD68 expression in cultured murine proximal tubular epithelial cells (mProx) stimulated by crude and pure BSA was examined by flow cytometry and immunofluorescence.', 'The tubular CD68-positive cells were observed on day 112. Immunoelectronmicroscopy revealed that some CD68-positive cells showed brush borders on the cell membrane and some of cytokeratin-positive tubular cells also expressed CD163 in mirror sections. The tubular CD68-positive cells were also positive for nitrotyrosine, gp91 (phox) and Rac 1. They contained lipid in their cytoplasm. Crude BSA, containing free fatty acid, induced CD68 expression in a dose- and time-dependent manner in mProx, but not pure BSA. The surface expression of CD68 was increased by high dose and long term stimulation with crude BSA as shown by immunofluorescence.'] Do tubular epithelial cells have the capacity to transdifferentiate into CD68-positive macrophage-like cells by oxidative stress?