An improved method for the immunocytochemical detection of bromodeoxyuridine labeled nuclei using flow cytometry

A new staining protocol is described for the immunocytochemical detection of BrdUrd labeled nuclei. Pepsin treatment of ethanol fixed cells or tissue, followed by DNA denaturation at low pH, resulted in increased sensitivity of BrdUrd staining comparable to the thermal denaturation protocol, and decreased background binding. This technique is applicable to cell suspensions, including cultured cells and bone marrow cells. Furthermore, pepsin digestion of ethanol fixed tissue fragments resulted in a high recovery of nuclei in which incorporated BrdUrd could be detected. This possibility, together with the high sensitivity, make this method especially suitable for cell kinetic studies of human solid tumors in vivo.